Add WASM detector observability and fix Latin hint routing

[dev-pi2pie]

Summary

This PR adds structured WASM detector observability across single-input and batch CLI flows, improves JSON/debug reporting, and fixes Latin hint handling/regressions in WASM mode.

Fixes #52

What changed

Detector observability

• added a structured detector debug model with summary counters and optional per-window evidence payloads
• added --detector-evidence for WASM runs, with compact and verbose debug output modes
• added a stable debug event envelope with:
  • schemaVersion
  • timestamp
  • runId
  • topic
  • scope
  • verbosity
• added detector evidence/debug report naming for autogenerated report files

CLI and batch integration

• threaded detector debug context through:
  • single-input runtime
  • async batch executor
  • worker-pool batch executor
• forwarded worker detector debug events back to the parent process
• added detector summaries to JSON output when --debug is enabled
• kept detector events file-scoped in batch mode and gated detector evidence behind --debug and --detector wasm

WASM detector quality and hint ordering

• deferred Latin hint application until after WASM detector routing so detector-derived locales are not overridden by a Latin tag hint
• preserved built-in and custom Latin hint subspans inside accepted WASM windows
• fixed hard-wrapped prose false negatives in the Latin quality gate by evaluating contiguous prose blocks instead of isolated physical lines
• preserved fallback relabeling behavior for unresolved Latin detector windows

Docs and contracts

• updated README, JSON output contract, and debug event stream contract
• added/updated plan, research, and job records covering:
  • detector evidence design
  • global debug observability
  • WASM Latin hint ordering
  • follow-up regression fixes
• bumped embedded/package version to 0.1.5-canary.3

Why

This branch improves visibility into WASM detector decisions without changing default output behavior for normal users, and it resolves correctness issues around Latin hint precedence and wrapped-prose detection.

Verification

• bun test test/word-counter.test.ts
• bun test test/command.test.ts

Notes

• debug JSON remains opt-in via --debug
• detector evidence remains opt-in via --detector-evidence
• batch worker and non-worker execution paths now have matching detector debug behavior