[P2] Preserve canonical IDs and user settings across mapping edits #175

Canonical identity is derived from tvg_id + guideNumber + name. Changing a mapping display name or guide number changes the identity, allocates a new UUID, and drops custom names and prior stream/guide choices. Output entries are restored by the same old identity, so their user settings are lost too.

Code: libs/canonical-channel-service.js#L109-L218. Reviewed 2026-09-06; these source files are unchanged between local 5ee8134 and GitHub main 0d923cf.

Evidence: Executing the actual rebuild function against an in-memory database, then changing a mapping name, produced a new canonical ID and reset custom_name to null.

Acceptance criteria:

• Anchor canonical identity to a stable persisted relationship independent of editable labels and guide numbers.
• Migrate/reconcile existing records while preserving profile positions/enabled state/overrides, custom names, preferred streams, and guide bindings.
• Define explicit merge/split behavior when mappings converge or diverge.
• Add repeated rename/renumber and reload regressions; preserve stable IDs exposed through MCP and HTTP.

Validation note: the local full test suite could not pass because the installed better-sqlite3 binary is incompatible with the available ARM64 Node runtime. Reproductions mentioned above use isolated dependencies and do not claim full application integration coverage.