feat: --auto flag to unlock auto/bypassPermissions modes

[BenSheridanEdwards]

Claude Code disables auto and bypassPermissions permission modes when ANTHROPIC_DEFAULT_*_MODEL is not a claude-* value. Default deepclaude exports the resolved backend name (deepseek-v4-pro etc.) so the gate stays locked and Shift+Tab reports "auto mode isn't available for this model".

This PR adds an opt-in --auto flag. When passed, set_model_env exports canonical claude-opus-4-7 / claude-sonnet-4-6 / claude-haiku-4-5-20251001 in place of the backend names. The proxy translates them back to the configured backend on the wire via MODEL_REMAP. The TUI's welcome chip will display the canonical name — that's the explicit, opt-in tradeoff for unlocking the gate.

Default behaviour is unchanged: backend names in env vars and TUI, no auto/bypassPermissions, no model remap fires.

Why opt-in

Surfacing the right tradeoff at launch matters because deepclaude's premise is cost savings — silently lying about the model in the TUI would mislead users about where their tokens are landing. With --auto, the user is asking for the gate to be unlocked; they accept the TUI showing a Claude name in exchange. With --auto off, everything stays honest by default.

The launch banner makes the tradeoff explicit either way:

# deepclaude
Auto mode: OFF (TUI shows 'deepseek-v4-pro')
  Pass --auto to unlock auto/bypassPermissions modes — TUI will then show 'claude-opus-4-7'.

# deepclaude --auto
Auto mode: ON
  TUI will display 'claude-opus-4-7' (auto/bypassPermissions unlocked).
  Actual routing: deepseek-v4-pro via https://api.deepseek.com/anthropic.
  Verify with: curl -s http://127.0.0.1:$PROXY_PORT/_proxy/cost | jq

A future PR will add a Claude Code statusLine integration so the actual backend (and live cost) is also visible at the bottom of the terminal — the natural counterpart to a TUI chip that lies under --auto.

What's in the diff

--auto core:

• AUTO_MODE global + --auto) arg parsing.
• set_model_env branched on $AUTO_MODE: canonical claude-* names under --auto, $RESOLVED_* otherwise.
• print_auto_mode_tip helper surfacing the tradeoff and the actual routing destination at launch (called from both launch_claude and launch_remote).
• --auto documented in show_help.

Proxy / launch foundation (active in both modes — not auto-mode-specific, but required for --auto to function):

• launch_claude now starts the local proxy and points ANTHROPIC_BASE_URL at it. Previously only --remote did this.
• start_proxy shared helper sets PROXY_PID/PROXY_PORT/PROXY_LOG as script globals; must be called without $() or the EXIT trap leaks the node child.
• SCRIPT_DIR is symlink-resolved so deepclaude works when installed via a ~/.local/bin symlink.
• start-proxy.js legacy mode accepts an optional [defaultMode] third argv so state.mode resolves to e.g. deepseek rather than _single and MODEL_REMAP[state.mode] actually fires.
• launch_claude deliberately does not touch ANTHROPIC_AUTH_TOKEN — whatever Claude Code is already carrying flows through; the proxy injects backend auth itself for non-image, non-Anthropic calls.

Adjacent proxy additions:

• MODEL_REMAP['fireworks'] block, mirroring the deepseek/openrouter entries, so --auto works on the fireworks backend.
• console.warn line in the existing remap branch when an inbound claude-* name has no MODEL_REMAP entry — drift detector for when Anthropic ships a new model and the table falls behind.

Test plan

• deepclaude (no --auto): TUI shows deepseek-v4-pro, Shift+Tab doesn't include auto/bypassPermissions, requests route through the proxy to DeepSeek.
• deepclaude --auto: TUI shows claude-opus-4-7, Shift+Tab cycles default → auto → plan → bypassPermissions, requests still route to DeepSeek (proxy log: model remap: claude-opus-4-7 → deepseek-v4-pro).
• Launch banner prints the appropriate auto-mode tip on both paths.
• curl http://127.0.0.1:$PROXY_PORT/_proxy/status reports "mode": "deepseek" (i.e. the defaultMode argv plumbing works); /_proxy/cost accumulates a deepseek bucket on each turn.

Notes

This PR overlaps with #21 on the proxy-in-path foundation (start_proxy, symlink-resolved SCRIPT_DIR, launch_claude routing through proxy, start-proxy.js [defaultMode] argv). When either PR merges first, the other can rebase onto main; git will recognise the duplicate patches and drop them. The auto-mode-only delta (~50 lines across deepclaude.sh and proxy/model-proxy.js) is what survives in this PR after such a rebase.