Qualify a focused browser release with save-migration and player-loop checks

## Priority

P2 — focused reliability or product improvement

## Context

Portfolio audit follow-up (2026-09-08). For this repository, focus on a small browser/PWA release and validate the core play loop, saved progress and performance before expanding systems. The separate local 3D adaptation is out of scope. Existing save export/recovery issues #3 and #8 are closed; this adds release qualification rather than claiming those features are absent.

## Starting points / evidence

Start from `client/src/components/game/HuntersPath.tsx`, current game hooks/modules and save-management UI. Coordinate accessibility work in #12.

## Implementation scope

Define a bounded playable slice using the current engine and a release checklist. Test new-player progression, reload/offline return and saved-data compatibility across a version change using synthetic saves. Set explicit browser/mobile performance budgets and prepare a small consented playtest protocol. Curate original mechanics/assets and document the provenance of shipped assets.

## Acceptance criteria

- [ ] A documented new-player path reaches a clear first milestone without developer intervention.
- [ ] Synthetic previous-version saves migrate without losing progress; invalid saves exercise existing recovery without overwriting recoverable data.
- [ ] Reload, offline return, export and reimport are tested through the actual UI.
- [ ] Representative desktop/mobile devices or clearly named emulations have measured loading/frame responsiveness against stated budgets.
- [ ] Playtest questions target clarity, enjoyment and return intent; findings are recorded only after actual sessions.
- [ ] Checklist and launch instructions apply only to this browser repository and do not require changes to local Unreal/Godot work.

Keep the change focused on this issue. Use synthetic fixtures for sensitive data and mocked providers for automated tests; do not require paid model calls to run the regression suite.

Start with client/src/components/game/HuntersPath.tsx, the current game hooks/modules, and the save-management UI to map the playable path and save flows. Use synthetic saves and mocked providers while exercising progression, reload, offline return, export, and reimport through the UI. Done means the browser-only release checklist, migration and recovery checks, performance budgets, playtest protocol, and asset provenance are documented and evidenced.

Written by the indexing model from the issue text.