Enhancement: Sync nav titles to Notion and improve rebuild_state matching

[virtualguard101]

Summary

Two related gaps affect long-term sync reliability:

1. Nav title changes do not update Notion page titles on sync (content/tags update only).
2. rebuild_state_from_wiki matches pages by title under parent, which breaks when titles collide or change.

Problems

• User renames a nav entry (e.g. section or page title); Notion still shows the old title.
• rebuild_state_from_wiki may bind the wrong page when duplicate titles exist under the same parent.
• Title drift makes manual recovery and debugging harder.

Proposed solution

Title sync on update/create

• When syncing a leaf or section, if nav title ≠ current Notion title property, PATCH the title property.
• Optional flag: --sync-titles (default on when cheap).

Rebuild matching improvements

• Prefer stable keys when available: prior state id, stored URL, or optional frontmatter notion_page_id.
• Fall back to title+parent matching with warnings on ambiguity.
• Log ambiguous match when multiple Notion pages share title under same parent.

Optional write-back

• After create/sync, optionally write notion_url to frontmatter or a sidecar field (config-gated).

Acceptance criteria

• Changing nav title updates Notion page title on next sync.
• Rebuild warns on ambiguous title matches instead of silent wrong bind.
• Docs describe matching priority order.

Related

• Structure reconciliation (section pages need title sync too)
• Git rename state migration (stable id mapping)