feat(lite): runtime kill-switch + staged-rollout gate (M5b)

Adds a fail-open, local-only gate that decides whether the lite wallet may run,
so a post-release issue can disable it and rollout can be staged — without any
phone-home (privacy posture: no runtime network fetch; the per-install rollout
bucket is a hashed, never-transmitted local id).

- wallet/lite_rollout_policy.{h,cpp}: a pure decision core. Order — emergency env
  kill-switch (absolute) -> local override -> manifest gates (global enable /
  version floor-ceiling / blocklist / staged-rollout permille) -> fail-open allow.
  Plus a JSON manifest loader (missing/invalid -> fail-open) and FNV-1a bucketing.
- Threads the decision through LiteWalletController -> LiteWalletLifecycleService:
  new availability() reason RolloutDisabled blocks create/open/restore and surfaces
  the gate's user-facing message via the lifecycle status.
- App::rebuildLiteWallet() resolves it from: DRAGONX_LITE_KILL_SWITCH (env), the
  lite_rollout setting (auto/force_on/force_off), and a locally-cached manifest at
  <config-dir>/lite_rollout.json. install id generated once via libsodium.
- Settings: persist lite_rollout override + the install id.

A signed remote fetcher can populate the manifest cache later without touching the
policy. Unit-tested (version compare, bucketing, override/env precedence, manifest
gates, staged rollout, loader fail-open, controller integration) and runtime-verified
on Linux (env kill-switch, manifest disable, control sync). Both variants build;
full suite passes; hygiene clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -71,7 +71,8 @@ Guard full-node-only code paths with `#if DRAGONX_LITE_BUILD` / chat code with `
 The Lite variant is **functionally complete and runtime-verified on Linux + Windows** (work lives on branch `cleanup/lite-plan-churn`, **local-only — not pushed yet**):
 - **Implemented:** lifecycle (create/open/restore + auto-open on startup), sync, refresh, send / shield / import / export / seed, persistence (the backend does *not* auto-save after sync/send/shield — the controller triggers `save` at those points), and passphrase **encryption** (encrypt/unlock/lock/decrypt + Settings UI + send-time & startup unlock; the backend locks immediately on `encrypt`). All controller-tested against the fake backend (`tests/fake_lite_backend.h`) and smoke-verified against the real SDXL backend via `tools/lite_smoke` (incl. a full sync). GUI is wired end-to-end with lite-appropriate wording; the full-node RPC connect loop / wizard / daemon strings are gated out of lite (lite "online" is derived from `lite_wallet_->walletOpen()`, not RPC).
 - **Packaging (verified):** `./build.sh --lite-backend --linux-release` (zip + AppImage) and `--win-release` (cross-compiled `.exe`; first build the Windows backend artifact with `scripts/build-lite-backend-artifact.sh --platform windows`). Both correctly exclude full-node assets.
-- **Remaining (M5b):** macOS packaging, CI backend-artifact build + signing, runtime kill-switch / staged rollout.
+- **Rollout / kill-switch (implemented):** `wallet/lite_rollout_policy.{h,cpp}` is a pure, fail-open gate (local-only, no network) feeding `LiteWalletLifecycleService::availability()` (new `RolloutDisabled` reason). Inputs: the emergency env var `DRAGONX_LITE_KILL_SWITCH` (absolute — not even `force_on` bypasses it); a `lite_rollout` setting (`auto`/`force_on`/`force_off`); and an optional **locally-cached** manifest at `<config-dir>/lite_rollout.json` (`global_enabled`, `min_version`/`max_version`, `blocked_versions`, `rollout_permille`, `message`) keyed for staged rollout on a hashed, never-transmitted per-install id. A signed remote fetcher can populate that cache later without touching the policy. Resolved in `App::rebuildLiteWallet()`; the disable message surfaces via the lifecycle status. Unit-tested + runtime-verified (env / manifest / control).
+- **Remaining (M5b):** macOS packaging, CI backend-artifact build + signing.
 - **To publish:** rename branch → `feat/lite-wallet`, base the PR on `dev` (the full-node UX is already there), and handle the dormant gated-OFF HushChat content bundled in commit `af06b8b`.
 
 The detailed milestone plan and design history (the v2 plan, backend artifact/ABI/signing design docs, the v1 plan, chat specs, etc.) are kept **untracked** under `docs/_archive/`.