feat(ingest): capture entity URLs from Markdown link embeds

[ntokaeva]

Problem

Forwarded Telegram posts of the form

📱 Смотреть на YouTube

are very common — channels write them as Markdown link embeds
[Смотреть на YouTube](https://youtu.be/...). Telegram delivers the
URL only on MessageEntity.text_link.url; the plain message text
holds the visible label without the link.

The current ingest pipeline reads only the visible body
(msg.text or msg.caption), so the URL is silently dropped. Anything
downstream (vault sync, transcript pipelines, search by URL) cannot
recover it.

Solution

New column notes.extracted_urls (idempotent migration, TEXT /
JSON array). On every ingest path that takes a message we now lift
URLs from both entities and caption_entities:

• text_link → entity.url
• url → slice of the visible text by offset/length

URLs are kept in document order, deduplicated, written as a JSON
array on the note row. NULL stays NULL on messages without relevant
entities so legacy rows and external tooling that doesn't know about
the column see no change.

Coverage

• src/bot/handlers/channel.py — text / web / youtube / document / post
• src/bot/handlers/media_group.py — albums; URLs merge across every
  message in the group
• src/core/ingest.py — ingest_text and ingest_document accept
  extracted_urls: list[str] | None
• src/core/notes.py — JSON (de)serialization, single mapper for SELECTs
• src/core/models.py — Pydantic Note.extracted_urls: list[str] | None

Tests

9 new cases in tests/test_entity_urls.py:

• text_link / url entities extracted from text + caption
• order preserved, duplicates dropped
• non-link entity types (bold, mention, hashtag) ignored
• migration adds the column on a fresh DB
• DB roundtrip with URLs returns the list intact
• DB roundtrip without URLs keeps the column SQL NULL (not the string "null")

Full suite: 440 passing.

Compatibility

• Migration is idempotent (_column_exists check), safe on running DBs
• Legacy code reading notes still works — the field is Optional
• Other callers (neighbors.py, sync_deleted.py) keep their own
  SELECTs without the new column; the field stays None via the
  Pydantic default
• No new dependencies

🤖 Generated with Claude Code