ci: split Build into required lint + advisory compile

[stevenjvik]

Why

The `Build` workflow has never gone green in CI. Going back to 2026-04-21, every run fails with 88 errors of the form `package com.minecolonies.api.entity.ai.statemachine does not exist`.

Root cause is not a regression — it's a CI architecture mismatch. `build.gradle` declares MineColonies as `compileOnly fileTree(dir: 'libs')` and `scripts/fetch-deps.sh` populates `libs/` from a local Minecraft instance (`$HOME/AppData/.../atm10/mods`). CI has no local Minecraft instance, no jar, no way to compile.

Full analysis + path-forward options at `audit/squire-mod-v2-ci-architecture-2026-05-09.md` in the vault. Picked option A (advisory CI, no third-party supply chain) over option F (CurseMaven proxy) — the latter resolves but adds a community-run external to the build path, not worth the trade for a personal mod.

What this changes

Splits the single `Build` job into two:

• `lint` (required signal) — runs `./gradlew help tasks` and `./gradlew dependencies`. Catches:

  • build.gradle syntax errors
  • Plugin version regressions (NeoForged moddev, etc.)
  • Broken Maven coordinates for declared deps
  • Gradle wrapper issues
  • Anything that doesn't need the MineColonies jar to detect

• `compile` (advisory) — `continue-on-error: true`. Runs the full `./gradlew build`. Cannot pass in CI without `libs/`, but stays in place so:

  • If you ever vendor the jars or switch to CurseMaven, this lights up immediately
  • Failure shows yellow on PRs instead of red — no more "ignored CI failure" cognitive load
  • Artifact upload still triggers if compile ever succeeds

Impact on Dependabot

5 stuck PRs (#12 #13 #14 #15 #16) currently red because the unified Build fails. After this lands, they show:

• ✅ Lint passes (real signal — the bump didn't break anything CI-detectable)
• ⚠️ Compile advisory failure (expected — same MineColonies-jar gap, not the bump's fault)

Steve can merge them based on lint signal + manual local verification, instead of staring at a permanently-red queue.

Local dev unchanged

`fetch-deps.sh` still works, `./gradlew build` still works on Steve's authoring machine. This is purely a CI workflow split.