chore(agent): sync-sweep rule on task completion + apply it; zram user docs

New standing rule (LOOP.md §5 step 4, echoed in AGENTS.md): when a task
ships, grep its number/feature name across agent/ and docs/ and update
or delete every cross-reference it made stale, in the same commit —
including pruning checked-off [x] HARDWARE-QUEUE entries whose outcome
is recorded (journal/ROADMAP; git history is the archive).

First application: BACKLOG PROPOSED groomed (the auto time-of-day theme
pitch was stale — shipped as #79; shipped/promoted placeholder lines
removed; v1.0 pointer rewritten; FUTURE promoted-stub dropped);
HARDWARE-QUEUE pruned of 29 checked entries (363→253 lines) with
dangling references reworded and the prune rule documented in its
header.

Also closes the zram user-doc gap: README §3 now documents the zram
default (zstd/50%/prio 100), hibernation working out of the box on new
installs, and the MIGRATION.md runbook for existing machines.

Verification: V0 (docs/meta only).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -330,6 +330,14 @@ the offending process (with a desktop notification) instead of freezing
 the desktop — process-level on purpose, since a Hyprland session is one
 cgroup and systemd-oomd would kill all of it (oomd is disabled
 accordingly). Opt out with `services.earlyoom.enable = false;`.
+**`zramSwap`** is also on by default (zstd, 50% of RAM, priority 100):
+day-to-day memory pressure pages into compressed RAM instead of the
+disk, keeping the disk swapfile free for **hibernation** — the installer
+creates a RAM-sized encrypted swapfile and wires `resume`, so
+Power › Hibernate works out of the box (swap size 0 at install = no
+swap). Opt out with `zramSwap.enable = false;`; to add hibernation to a
+machine installed before it existed, follow
+**[docs/MIGRATION.md](docs/MIGRATION.md)** § Enabling hibernation.
 
 ## 4. How theming works