fix(tdp-control): persist user-set TDP across shutdown (#204)

[srsholmes]

Problem

The manually-set TDP lived only in memory, so the user's choice was lost on
every reboot — hardware power limits reset to firmware defaults on shutdown.

Fix

Persist the last user-requested wattage to the plugin config file
(~/.config/loadout/plugins/tdp-control.json, manualTdp key) and re-apply it
on startup. Only user-initiated setTdp() / applyProfile() calls persist —
automatic applies (per-game profiles, AC transitions, resume, device changes)
route through a private applyTdp() and leave the saved value untouched.

The "no game" TDP model

The saved manual TDP is the authoritative "no game running" value, and is
restored regardless of whether per-game profiles are enabled. Precedence:

• A recognized per-game profile's game launches → that profile's TDP wins.
• No game running (boot, game exit, or a game without a profile) → the
  saved manual TDP is applied.
• The engine's stored defaultTdp remains only as a fallback for users who
  never set a manual value.

Implemented via a getNoGameTdp callback injected into the profile engine, so
handleGameExit, the no-profile branch of handleGameLaunch, removeProfile,
and the per-game toggle-on path all resolve the same no-game value.

Note: this supersedes the earlier "manual restore only runs when per-game is
off" behavior — with per-game on, boot previously fell back to the engine
defaultTdp and silently dropped the user's manual value (e.g. set 35W, got
12W after reboot).

Guard against in-game drift

setTdp() does not overwrite the saved no-game value while a per-game
profile is actively governing TDP (per-game enabled + a game running). In that
state the slider tunes the running game's profile (the frontend routes it to
setGameProfile), so persisting there would let an in-game tweak silently
redefine the value restored on game exit / reboot.

Tests

Added regression coverage for the getNoGameTdp paths (exit, no-profile launch,
profile precedence, removeProfile, toggle-on, null/omitted-callback fallback)
and the setTdp in-game persistence guard. 90/90 tdp-control tests pass;
typecheck clean.

Verification

Built and installed on hardware (OneXPlayer APEX / Ryzen AI MAX+ 395). Service
logs confirm Restoring saved manual TDP …W on startup where it previously
applied the 12W per-game default.

Co-Authored-By: Claude Opus 4.8 [email protected]
Claude-Session: https://claude.ai/code/session_01XNKJxF3QuZjhsjn5CqKyJM