Catch up characters from Chronicle's change feed

[keyxmakerx]

Fixes: none
Security implication: none. It uses the same feed route and API key as the journal catch-up (GET /sync/changes, which needs an owner key). Nothing is deleted: a removed character only unlinks its actor.
Consumer-verified: Chronicle internal/plugins/syncapi change feed (/sync/changes, merged in #957 and earlier) and GET /entities/:id; the bench exercises both against Chronicle main at 82578dd.
Foundry compatibility: n/a. No new Foundry API is used; it runs through the same actor update/flag calls as before. Not live-checked in a Foundry world (#94).
Mockup: n/a, nothing on screen changes.

What this changes

Before: every time Foundry connected, it listed every character in Chronicle and rewrote each linked actor, even when nothing had changed.

After: on connect, linked actors catch up only on the characters the change feed says changed. An actor already at Chronicle's version is left alone, including on the full walk. Reopening a world with nothing new writes nothing. A character deleted in Chronicle unlinks its actor and keeps it. An older copy never rolls an actor back.

Why

This is step 3 of the agreed Foundry sync rebuild, characters after journals (module #125). The hard requirements were no duplicate copies, changes that are safe to repeat, and a passing two-sided bench before anything is called ready.

• scripts/actor-sync.mjs:
  • adds feedArea = 'actors' and feedActive();
  • in delta mode, onInitialSync({feed}) calls _catchUpFromFeed;
  • _atVersion and _olderThanRecorded guard every apply;
  • a failure throws, so the shared cursor is not saved and the next connect replays.
• _notifySyncIssues({quick}) counts unlinked actors locally on a delta connect instead of listing all of Chronicle. That listing was the remaining full walk on reopen.
• bench/scenario.mjs holds the shared bench helpers. assertHealthy now also fails on duplicate actors, and on a character that exists as both an actor and a journal.

Deviation: an untouched character listed in the feed is still fetched once, by design: the feed carries ids, not versions. The bench asserts data writes only, because Chronicle publishes a stale updated_at after a fields update, which can cause a harmless flag-only rewrite. That is filed on keyxmakerx/Chronicle#985.

Test plan

• node --test tools/test-*.mjs: 1023 tests, 1023 pass, 0 fail, with module main (Player notebook and Jot notes tab in Foundry #126) merged in (5 new in tools/test-actor-feed.mjs)
• node tools/check-package-descriptor.mjs: n/a, the descriptor is unchanged
• Manual verification in Foundry: not done (no Foundry runtime here; live checks tracked in Live test session on Foundry v14 (after TESTING.md is brought up to date) #94)
• If UI-touching: n/a
• CHRONICLE_DIR=../Chronicle bench/run.sh against Chronicle main (82578dd), rerun after merging module main: 16 of 16 scenarios pass, 4 of them new for characters:
  • live create makes one actor and no journal;
  • offline changes arrive from the feed, and a second open writes nothing;
  • a deleted character unlinks its actor and keeps it;
  • a Foundry HP edit is pushed once and not re-applied on reopen.
• CI passes

Tenet self-check

• T-B1 security: no new route or token handling; nothing is deleted without asking
• T-B2 plugin isolation: changes stay inside the module
• T-B3 production UI: n/a
• T-B4 dual-audience docs: .ai.md, CLAUDE.md and bench/README.md now say journals and characters use the feed

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