Archive inactive tribes

[caydyan]

Summary

• add a daily inactive-tribe archive job that unlists tribes whose recorded last_active is older than the configured cutoff
• default the cutoff to 30 days and allow TRIBE_ARCHIVE_AFTER_DAYS to override it, with non-positive values disabling the job
• only archive listed, non-deleted tribes with last_active > 0 so legacy rows without activity data are not hidden blindly
• add regression coverage for stale, recent, legacy, already-unlisted, and deleted tribes
• update the generated database mock for existing GetBountyByUnlockCode interface compatibility so package tests compile

Fixes #292
Fixes #293

Validation

• go test ./... -run '^$'
• git diff --check
• go test ./db -run TestArchiveInactiveTribes -count=1 could not run locally because the documented test Postgres at localhost:5532 was unavailable; attempts to start docker/testdb-docker-compose.yml failed because Docker could not start Postgres containers in this environment.

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[caydyan]

Current-head validation rerun on e95bfc8:

• go test ./... -run '^$' passes across packages as a compile/no-test sweep
• git diff --check origin/master...HEAD passes

I also attempted the focused DB regression test:

• go test ./db -run TestArchiveInactiveTribes -count=1 -v

That test is still blocked locally because the documented test Postgres is not running on localhost:5532 (connect: connection refused). The repo README points this path at docker compose -f docker/testdb-docker-compose.yml -p test_db up -d; Docker is installed here, but the local Docker daemon API currently returns a 500 on docker ps, so I could not bring up the test DB in this environment. No touched-file compile diagnostic was reported by the passing package compile sweep.