Fix circular import, primary-admin NULL trap, and add gateway quota reset

Restores a working import graph and closes two data-correctness bugs, plus
adds a reset for the AI gateway's rolling 24h spend.

Circular import: database/__init__ -> engagement -> content -> utils ->
database made the package unimportable. get_project_devlog moves out of
database/engagement.py into content.py, where enrich_items already lives.

Primary administrator: _can_hold_primary_admin read is_active with
bool(row.get("is_active")), so an admin row whose is_active column is SQL
NULL (any row predating the column) was treated as deactivated and skipped.
Every other site defaults an unknown is_active to active; this one now does
too.

Profile JSON: xp_next_level and xp_progress_pct were computed but only put on
the top-level context, never on profile_user, so they serialised as null even
though UserOut declares them and the API docs document them as embedded there.

Gateway quota reset: a cap previously lifted only with the passage of time.
quota.reset upserts a watermark row into gateway_quota_resets, scoped by the
same three nullable dimensions as a quota rule, and spent_24h sums from
max(24h cutoff, watermark). No ledger row is deleted, so the cost analytics on
/admin/ai-usage stay intact. Reaches every surface: POST
/admin/gateway/quota-resets, a per-rule Reset spend button, the Devii tool
gateway_quota_reset (confirm-gated), devplace gateway quota reset, and the API
docs. Admin's Reset all quotas now stamps a global gateway watermark too,
which is what a caller stuck on "AI gateway daily quota exceeded" needed.

Startup: _backfill_gamification swept every xp=0 user on every boot in every
worker and could never converge, since a user with no content earns no XP.
It now intersects pending users with _milestone_candidates(). db.tables is a
live reflection, so it is hoisted out of the loops that probed it per row.

Docker: the dependency layer now depends on pyproject.toml only, so a source
edit no longer reinstalls every dependency and re-downloads Chromium.
Adds start_interval so the healthcheck probes during the start period, and a
docker-reload target, since docker-up does not restart an unchanged container.

Adds events.md, the audit event catalogue that README, CLAUDE.md, the quiz
docs and the tooling all referenced but which never existed: 288 keys across
28 categories, including the families built from a variable at the call site.

Test fixes: both devlog helpers dated post 0 as the newest while the tests
assumed post 2 was; a profile login posted username= to a form that takes
email=; a devlog assertion matched six buttons under strict mode; and the
primary-admin tests seeded founders newer than the back-dated fixture admin,
so they only passed without the api tier.

Full suite: 2989 passed, 1 skipped.

tests/api/profile/index.py

@@ -234,7 +234,6 @@ def test_activity_comment_url_matches_notification_target(app_server):
 
 
 def test_activity_post_exposes_url(app_server):
-    from datetime import datetime, timezone
     from devplacepy.database import get_table, refresh_snapshot
 
     owner = _seed_owner()
@@ -417,7 +416,7 @@ def test_own_profile_json_exposes_xp_fields(app_server, seeded_db):
     session.post(
         f"{BASE_URL}/auth/login",
         data={
-            "username": seeded_db["alice"]["username"],
+            "email": seeded_db["alice"]["email"],
             "password": seeded_db["alice"]["password"],
         },
         allow_redirects=True,