feat(keys): LH_IGNORE_ENV_KEYS — the fresh-user switch + dev-fresh launcher

The owner needs exact new-user simulation as a one-command launch
(repeatable first-run BYOK testing). Option A, owner-approved:
env-hiding switch + launcher script.

Fix 1 — LH_IGNORE_ENV_KEYS=1 in the keys seam: when set, every env key
is invisible app-wide; only auth.json counts. The mechanism is boot-time
DELETION, not seam-local filtering: pi-ai resolves provider keys from
process.env NATIVELY at every request (verified — auth/context.js's
defaultProviderAuthContext reads live env, no boot snapshot), so
deleting the managed vars from process.env in initAuthEnv is the ONE
mechanism that hides keys from every consumer — model engines included,
plus the three direct process.env readers (visual-maker, pdf-reader,
openRouterApiKey). realEnv stays EMPTY under the switch (nothing counts
as env), and the fill-gap still reflects auth.json keys so a fresh user
can add keys mid-session and engines see them with no restart.
keyValue reads file-only under the switch as belt-and-suspenders (a
post-boot env reintroduction stays invisible to the seam). Unset
switch = today's behavior, byte-for-byte (server-keys.test.ts pins it).

Fix 2 — scripts/dev-fresh.sh (npm run dev:fresh): fresh throwaway
LH_DATA_DIR (.fresh-data/, wiped each launch, --keep preserves), and —
the subtle bit — LH_AUTH_FILE redirected INTO the fresh dir: dev's
AUTH_FILE default is the repo-root auth.json, which may symlink the
real keys; the fresh instance must never see it. Sets the switch,
dedicated port (default 3005, --port overrideable, standing assignments
3000-3004 refused), prints URL + data dir, safe to rerun. .fresh-data/
gitignored.

Test: tests/fresh-env-keys.test.ts (own process — the switch is
boot-time): the engine-path deletion asserted directly, the env/file
collision resolved to the file, status rows report file sources only,
mid-session saveKey/deleteKey round-trip, idempotent re-init, and the
unset-switch env-wins read seam live-checked.

Live-verified on 3005 via the launcher: zero federated models, all
providers keyPresent false, no present keys, no auth.json/settings.json
in the fresh dir; then mid-session ZAI save → 7 zai models federate
instantly, source 'file' — while .env.local's real keys stayed
invisible throughout.

Gates: typecheck, lint, 863/863, build.

package.json

@@ -13,6 +13,7 @@
 		"lint": "eslint .",
 		"typecheck": "tsc --noEmit",
 		"desktop:dev": "concurrently -k \"next dev\" \"LH_DEV_URL=http://localhost:3000 electron .\"",
+		"dev:fresh": "bash scripts/dev-fresh.sh",
 		"desktop:dist": "next build && node scripts/build-server.mjs && electron-builder --mac --arm64"
 	},
 	"dependencies": {