feat: add Flutter-aware Pickforge doctor

[ElbertePlinio]

Summary

• add an experimental, unpublished Rust pickforge doctor [--project-dir <path>] [--json]
• detect Flutter projects, Flutter/Dart tools, Claude/Codex/Pi harnesses, and the prospective per-project state path without executing tools or writing state
• preserve PickLab's TypeScript project-ID contract across symlinks, dot segments, Windows verbatim paths, and non-UTF-8 failure boundaries
• add deterministic human/JSON reports, readiness-based exit codes, tests, release notes, and Linux/Windows Rust CI

Validation

• cargo fmt --check
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo test --workspace --locked — 29 passed on Linux
• cargo check --workspace --all-targets --locked --target x86_64-pc-windows-msvc
• cargo clippy --workspace --all-targets --locked --target x86_64-pc-windows-msvc -- -D warnings
• fake-Flutter smoke verified schema v1, readiness, no state creation, and a clean fixture Git tree
• bun run typecheck, bun run lint, and bun run build
• local full Bun suite: 1,082 passed, 44 skipped; 8 existing desktop-session tests could not run because this machine lacks Xvfb/x11vnc/xdotool/xterm (installed by CI)

Review and scope

• local-review risk class: serious backend
• correctness/conformance, security/dependency/CI, and simplification/test-integrity panels completed; targeted verification found no remaining P0–P3 findings
• PR 1 of the six-PR alpha plan in Build the Flutter-first Pickforge integration alpha #64; remaining slices build transactional init, adapters, MCP migration, Flutter workflow, and evidence packaging on this foundation
• no config writes, network calls, telemetry, MCP changes, TypeScript behavior changes, release exposure, repository rename, or archival

Not tested

• macOS Rust behavior
• packaging or distribution of the Rust binary
• Windows-native execution pending this PR's CI matrix

Refs #64