docs: refresh 7 stale module headers that describe shipped work as "later phase" (E3 S3, B-core-12)

This codebase leans on "why" comments as its architecture doc, so a header that
claims the opposite of the code below it is worse than none. Fix the seven the
review flagged: channels.py (subscribe/unsubscribe shipped), playlists.py +
sync/playlists.py (YouTube two-way sync + write-back shipped), setup.py (drop the
"epic 6c" ref — the wizard steps exist), config.py ("auth._client_ip" ->
"routes.auth._client_ip"), db.py ("routes/plex.py" -> "routes/plex/" after the
package split), sysconfig.py (the "Phase C" note — the watch-sync job that reads
plex_watch_sync_interval_min has landed; clarified it's a boot default, not a knob).
Docs only.

backend/app/config.py

@@ -57,7 +57,7 @@ class Settings(BaseSettings):
     # VPS Caddy front door. A request from any other peer (someone hitting the app port directly)
     # is NOT trusted and its raw socket IP is used, so it can't spoof its rate-limit identity via
     # XFF. Empty = trust no proxy (use the direct peer) — correct for a directly-exposed / local-dev
-    # deploy. Comma-separated. See auth._client_ip + the deploy docs.
+    # deploy. Comma-separated. See routes.auth._client_ip + the deploy docs.
     trusted_proxy_ips: str = ""
 
     # --- Outbound email (onboarding: access-request + approval notices) ---

backend/app/db.py

@@ -12,7 +12,7 @@ class Base(DeclarativeBase):
 
 # Pool sized above the sync-endpoint threadpool (~40) so a burst of short DB sessions can't starve on
 # checkout. The image proxies deliberately DON'T hold a connection during their slow external fetch
-# (see routes/plex.py), so this headroom is only for the many brief sessions, not long ones.
+# (see routes/plex/), so this headroom is only for the many brief sessions, not long ones.
 engine = create_engine(
     settings.database_url,
     pool_pre_ping=True,

backend/app/routes/channels.py

@@ -1,6 +1,6 @@
 """Channel manager: the user's subscriptions with their personal overrides (priority,
-hidden, tags) and per-channel sync state. Read + local-write only — YouTube-side writes
-(unsubscribe) live behind the optional write scope and are added in a later phase."""
+hidden, tags) and per-channel sync state. Local reads/writes plus YouTube-side writes
+(subscribe / unsubscribe) that require the optional write scope."""
 import logging
 from datetime import datetime, timezone
 

backend/app/routes/playlists.py

@@ -1,6 +1,7 @@
-"""Local playlists: per-user named, ordered collections of videos from the shared
-catalog. Foundation phase = local only (create / rename / delete, add / remove / reorder
-items). YouTube two-way sync (mirror existing playlists, push edits) lands in later phases."""
+"""Playlists: per-user named, ordered collections of videos from the shared catalog. Local
+CRUD (create / rename / delete, add / remove / reorder items) plus YouTube two-way sync —
+mirror the user's own YouTube playlists in (`/sync-youtube`) and push/revert local edits back
+out (`/{id}/push-plan`, `/{id}/revert-youtube`), behind the optional write scope."""
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
 from sqlalchemy import func, select, and_

backend/app/routes/setup.py

@@ -3,7 +3,7 @@
 `GET /api/setup/status` is public (the SPA uses it to decide whether to show the wizard). Every
 mutating step goes through `require_setup`: it rejects once the instance is configured AND requires
 the one-time setup token (printed to the container logs at first boot, carried by the wizard as the
-X-Setup-Token header). The wizard steps themselves are added in epic 6c.
+X-Setup-Token header).
 """
 from typing import Any
 

backend/app/sync/playlists.py

@@ -1,6 +1,6 @@
-"""Read-direction YouTube playlist sync: mirror each user's own YouTube playlists into
-local `source='youtube'` playlists (kept fresh by the scheduler). One-way (YT -> local);
-the write-back direction (local edits -> YouTube) is a later phase.
+"""YouTube playlist sync, both directions. Read: mirror each user's own YouTube playlists
+into local `source='youtube'` playlists (kept fresh by the scheduler). Write-back: push local
+edits out to YouTube (`plan_push` / `push_playlist`), behind the optional write scope.
 
 YouTube's special Watch Later / History playlists are not exposed by the Data API and are
 never synced. Videos in a playlist that aren't in our shared catalog yet are fetched and

backend/app/sysconfig.py

@@ -96,8 +96,8 @@ SPECS: tuple[ConfigSpec, ...] = (
     ConfigSpec("plex_overlay_map", "str", "plex", "plex_overlay_map"),
     # (plex_sync_interval_min is tuned from the Scheduler dashboard, not here — it's a scheduler job.)
     ConfigSpec("plex_max_transcodes", "int", "plex", "plex_max_transcodes", min=0, max=16),
-    # NOTE: plex_watch_sync_interval_min (config.py default) is surfaced here in Phase C, when the
-    # incremental watch-sync scheduler job that reads it lands.
+    # NOTE: plex_watch_sync_interval_min is a config.py default read by the watch-sync scheduler job
+    # (scheduler.py); it is intentionally NOT a runtime admin knob, so it stays out of SPECS.
 )
 
 _BY_KEY: dict[str, ConfigSpec] = {s.key: s for s in SPECS}