Make actor template resync interval configurable

[Eitan Yarmush (EItanya)]

Actor template discovery currently uses a fixed 20-second resync interval. This PR adds --template-resync-interval so deployments can tune that delay, preserving the 20s default and rejecting nonpositive values. The setting also controls the reconciler's existing fallback retry delay.

This is intentionally a small change to start a discussion about how template builds should be dispatched as the template catalog grows.

The current resync fetches and decodes every template, including completed ones. At 100,000 templates, a 20-second interval implies roughly 5,000 template rows read per second per replica, assuming scans finish quickly. This is an estimate from the code, not a benchmark.

Possible follow-ups:

• Immediate enqueue: start work after creation, retaining a slower recovery scan for crashes between persistence and enqueue.
• Outbox/watch: consume changes instead of scanning the catalog. The existing worker outbox still polls every 50 ms and broadcasts events to each subscriber; write overhead and recovery scans need consideration.
• Durable pending-build queue: atomically record work, claim due jobs using short FOR UPDATE SKIP LOCKED transactions, and recover expired leases. This still polls, but queries pending work rather than the full catalog. LISTEN/NOTIFY is not the proposed default because it serializes notifying commits.
• Imperative build / long-running operation: give callers explicit build control or a progress/completion handle. Either still needs reliable execution underneath.

The main question is whether template builds need a broadcast change feed or a queue where replicas claim different jobs. Neither alternative is implemented here.

Full research: database costs, execution options, recovery requirements, and sources.

Validation: all Go race tests and repository verifiers passed using module mode with NO_COLOR unset. CLI checks confirmed the default and rejection of zero/negative intervals; the existing reconciliation test checks a custom interval.

Fixes #<issue_number_goes_here>

It's a good idea to open an issue first for discussion.

• Tests pass
• Appropriate changes to documentation are included in the PR