fix: reconcile task progress after each item

[tt-a1i]

Summary

Fix session tasks that stay visually stale when a model completes several user-supplied items without reconciling each status.

• teach the model to mark each tracked item in_progress before work and reconcile its real outcome immediately
• require a final reconciliation of tasks touched by the current request
• return the complete bounded current snapshot after every add/update, so the next item remains explicit
• preserve task-scoped evidence semantics: commit/test/authorization signals never infer completion
• add a four-task regression proving every explicit transition rewrites the widget and advances the persisted revision

This supersedes the heuristic signal-reminder direction in #6 without merging regex-based completion inference.

Verification

• bun install --frozen-lockfile
• bun run check
• bun run test — 593 Node tests + 29 Vitest tests
• focused task suite — 41 tests
• real Pi/model E2E — exact sequence tasks_add, then in_progress/done for T1–T4; revisions 1–9; final batch reset
• npm pack — 121 files, no tests/specs/tsconfig; only the three task runtime files shipped
• clean packed Pi load — PACKED_PI_TASKS_LOAD_OK
• git diff --check
• read-only reviewer — no findings