perf(web): retry-harden the one-time conversion VACUUM against reloads

[crs48]

Problem

The one-time conversion VACUUM (apps/web/src/lib/db-vacuum.ts, exploration 0260, follows #380/#381) converts long-lived profiles to auto_vacuum=INCREMENTAL. It is scheduled via runWhenBootSettled (first paint + 3 s settle + idle), so on a bloated ~500 MB profile with ~19 s first paint it starts ~25–30 s after open and takes 1–3 minutes on the single serial SQLite worker. VACUUM is atomic: a reload or tab close mid-run rolls it back with zero progress. The slowness it exists to fix is exactly what makes users reload — observed 2026-07-05: 5 rapid reloads — so the file never converts and cold opens stay ~17–19 s forever.

Fix — graduated escalation off a persisted attempt counter

• Attempt counter xnet:db-vacuum:attempts (localStorage): incremented the moment a real VACUUM starts, cleared on success. Skipped runs (in-memory DB, flag latched + PRAGMA auto_vacuum=2) never touch it — steady state stays one idle PRAGMA read per boot, and first paint is never blocked.
• 2nd attempt on (one prior interruption): a subtle non-blocking pill — “Optimising storage — keep this tab open a few minutes” — shows while the VACUUM is in flight and clears on completion or failure (StorageOptimiseHint, wired via the same window-CustomEvent bus pattern as storage-durability.ts). Placed bottom-20 right-4 to clear the compact-shell bottom nav, the UndoToast, and the dev-tools launcher (verified on both form factors in preview).
• 3rd attempt on: scheduling escalates — the VACUUM starts right at first paint (bootSettled()), skipping the 3 s settle + idle wait, with the same 45 s no-paint fallback as runWhenBootSettled. One deliberately slow-feeling boot in exchange for finally landing the conversion.
• A failed (thrown) VACUUM keeps the counter, so crash-loops escalate the same as reload-loops.

Drive-by fix: <Presence> exits never ran in the app

Nothing in apps/web imported @xnetjs/ui/motion.css — only Storybook did. <Presence> unmounts on animationend, so with no keyframes loaded every Presence-wrapped element stayed mounted forever once shown (e.g. UndoToast never left the DOM after its 6 s timeout). globals.css now imports motion.css; verified live that the exit rules load and the pill unmounts on animationend.

Verification

• 8 new unit tests in db-vacuum.test.ts (counter persist/clear/keep-on-failure, no counting of skipped runs, escalated start at first paint + no-paint fallback, hint publish/clear incl. failure path, no hint on first attempt) — 12/12 pass; full suite 10096/10096.
• Live preview: with attempts=1 pre-set, the real path ran end-to-end (db vacuum done logged, counter cleared, flag latched); pill verified on desktop + mobile clear of all bottom-edge occupants.
• tsc --noEmit, prettier, check-motion-vocab, check-humane-patterns, and a production vite build all pass.
• Note: pushed with --no-verify after running every pre-push step manually — the hook's own pnpm install flips core.bare=true inside a git worktree and breaks the git calls that follow it.

🤖 Generated with Claude Code

[github-actions]

🖼️ UI changes in this PR

No visual differences detected in the changed UI.

_{CI run}

[github-actions]

Preview removed for PR #383.