fix(tasks): synchronize file updates with SQLite and FTS

[fallintoplace]

Summary

• persist the final task state after applying file-backed updates
• keep deadline metadata and full-text search synchronized with Markdown files
• preserve status and tag metadata updates when no task file is changed

Problem

task_update refreshed SQLite and FTS only inside the title-update branch, before applying the remaining changes. This left three stale-state paths:

• deadline-only updates changed Markdown but not the database deadline
• note-only updates were absent from search
• combined title and note updates indexed the content before the note was appended

Deadline sorting, escalation, the tasks UI, and search could therefore disagree with the task file until a later reindex.

Fix

The handler now applies all requested file changes first, writes the final Markdown, and then performs one upsert with the final title, status, deadline, tags, and content. Metadata-only updates keep their existing fallback path.

Tests

Regression coverage verifies deadline-only updates, note indexing, and a combined title, status, deadline, tags, and note update.

• task-status suite: 21 passed
• database and task-status suites: 127 passed