Add Simplified Chinese README, link from the language switcher

[jumincho]

Summary

Add a Simplified Chinese README and wire it into the language switcher.

• README.md: KO/EN switcher line now also surfaces [中文](./README.zh-CN.md). Otherwise unchanged.
• README.zh-CN.md (new): Simplified Chinese mirror of the same structure (overview · features · screens · stack · layout · secrets · build · materials · license).

Code intentionally left alone

The Android source here is already a clean reverse-engineered shape:

• Package: com.jumincho.beatingyesterday (not com.example.*).
• data/ (FoodCalorieApi, Note, NoteAdapter, NoteDatabase) + ui/ (ProfileSetupActivity, home/, diet/, productivity/CircularTimerView) sub-packages — proper data-layer / UI-layer separation.
• build.gradle already reads FOOD_API_KEY from local.properties (with env-var fallback) and throws a clear GradleException at configure-time if it's missing — better than silently building with an empty key that fails later at runtime.
• Java class names follow PascalCase + the Activity / View / Adapter / Database suffix where appropriate.

So this PR is README-only.

Suggested GitHub repo metadata (please apply manually in Settings)

GitHub's MCP server has no update_repository tool, so the following can't be done from this PR — but here are the values I'd suggest:

• Repo name: keep as beating-yesterday (already evocative).
• About (one-liner): Android self-improvement app that frames each day as a contest with yesterday's calorie + study record (Korea Food Safety OpenAPI, BMI-aware scoring).
• Topics: android, java, self-improvement, bmi, food-safety-korea, openapi, sqlite, material-design, fragment, viewmodel

Test plan

• README renders with 中文 link working.
• README.zh-CN.md renders correctly on GitHub.
• No source files touched — ./gradlew assembleDebug should be unaffected.

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Generated by Claude Code

[jumincho]

Follow-up file-level inspection — per-file changes

After the initial README + HomeViewModel BMI-constants commit, a deeper bottom-up read of every file under app/src/main/java/com/jumincho/beatingyesterday/ surfaced more cleanups. Each follow-up is its own commit grouped by concern so the PR stays bisectable.

fe1ed06 — BMI level magic numbers, daily-kcal baselines, fragment null-guards

• app/src/main/java/com/jumincho/beatingyesterday/ui/diet/WeightManagementFragment.java
  • Switched HomeViewModel.bmiLevel == 1/2/3 to use BMI_LEVEL_UNDERWEIGHT / NORMAL / OVERWEIGHT (defined in HomeViewModel earlier in this PR but not yet consumed).
  • Pulled the gendered daily-calorie baselines 2700 / 2000 into STD_KCAL_MALE / STD_KCAL_FEMALE with a comment noting the 2020 KDRI source.
  • Added a if (activity == null) return; guard in the click listener and wrapped the Today_kcalScore SharedPreferences write so a fragment that's been detached during this onCreateView won't NPE.

37140031 — FoodCalorieApi URL fragments, timeouts, response checks

• app/src/main/java/com/jumincho/beatingyesterday/data/FoodCalorieApi.java
  • Pulled the API host, service id (I2790), response format, paging window, kcal field name (NUTR_CONT1), and the localized success message (정상처리되었습니다.) into named private static final constants.
  • Named the two 10000-ms timeouts as CONNECT_TIMEOUT_MS / READ_TIMEOUT_MS.
  • Hardened the success check to optString("MSG", "") so a malformed response can no longer throw inside the success path.
  • Added a class-level // TODO(modernize): flagging that the raw HttpURLConnection + JSONObject + bare Thread pattern is the obvious candidate for a Retrofit + Gson + structured-threading rewrite — left for a follow-up because it would touch the build script and the DietInputFragment call site.

97ab43e5 — Null-guard (MainActivity) getActivity() casts across fragments

• app/src/main/java/com/jumincho/beatingyesterday/ui/diet/DietFragment.java
• app/src/main/java/com/jumincho/beatingyesterday/ui/diet/DietInputFragment.java
• app/src/main/java/com/jumincho/beatingyesterday/ui/productivity/ProductivityFragment.java
  • Fragment#getActivity() is documented to be nullable. Each fragment's click listener was doing an unchecked downcast to MainActivity and then calling a method on it — an NPE waiting for a click that races with detach. Added a plain if (activity == null) return; early-out at the top of each listener. ProductivityFragment also stops calling getActivity() twice (once for the cast, once for the Intent context) and reuses the resolved reference.

43a95271 — NoteDatabase schema constants final

• app/src/main/java/com/jumincho/beatingyesterday/data/NoteDatabase.java
  • DATABASE_NAME / TABLE_NOTE / DATABASE_VERSION were public static (mutable) but read everywhere as if they were compile-time constants. Marked them final so a caller can't accidentally reassign the table name mid-run.

cde54594 — CircularTimerView Handler message codes + modernize TODO

• app/src/main/java/com/jumincho/beatingyesterday/ui/productivity/CircularTimerView.java
  • handleMessage's switch was branching on the raw integers 1 / 2 / 11 / 12 with the convention "1-series = countdown, 11-series = stopwatch" implicit in three separate methods. Renamed to MSG_TIMER_TICK / MSG_TIMER_DONE / MSG_STOPWATCH_TICK / MSG_STOPWATCH_DONE so all three call sites read the same way.
  • Pulled the 100ms tick period and the 1000ms initial delay into TICK_INTERVAL_MS / TIMER_INITIAL_DELAY_MS.
  • Pulled the 5 / 59 / 59 hour-minute-second clock-domain maxima (used by isMaxTime() and the setStartTime() guard) into MAX_HOUR / MAX_MINUTE / MAX_SECOND.
  • Added a // TODO(modernize): at the Handler block noting that this would be a CountDownTimer or a lifecycle-scoped coroutine flow in a modern Android build, but rewriting it would touch TimerActivity and the listener interfaces and would need new dependencies — out of scope for the file-level pass.

120159ca — ProfileSetupActivity question-state machine + SharedPreferences keys

• app/src/main/java/com/jumincho/beatingyesterday/ui/ProfileSetupActivity.java
  • The setup flow is a 6-state machine (name → gender → age → height → weight → done) but the dispatch was a chain of questionFlag == 0/1/2/3/4 branches with no in-file documentation of which number meant which question. Named them QUESTION_NAME … QUESTION_DONE.
  • Pulled the "UserData" SharedPreferences container and the six column keys ("Flag" / "Name" / "Gender" / "Age" / "Height" / "Weight") into private static final strings so a typo on the (string-keyed) load/save path is a compile error instead of a silent default-value read.

Out of scope / intentionally not touched

• Note.java's _id field (Android BaseColumns._ID = "_id" SQL-column convention — not arbitrary inconsistency).
• The Integer.valueOf(displayNumberHour) != … pattern inside CircularTimerView#getDisplayNumber (autoboxing comparison is suspicious but rewriting it changes behavior on the hot draw path — deferred).
• MainActivity's "UserData" SharedPreferences key duplication (covered by the ProfileSetupActivity constant — promoting to a shared Prefs helper is a follow-up because it touches HomeFragment and would need its own commit).
• Threading rewrites (FoodCalorieApi Thread, CircularTimerView Handler+Timer): tagged with // TODO(modernize): per instructions, not rewritten in this PR.

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Generated by Claude Code

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Generated by Claude Code