Add Hartwood: Emberwatch browser game (server, UI, core, tests, PLAN)

[MTeague86]

Motivation

• Implement the documented plan to build a single-screen browser survival game with deterministic game-state utilities, a responsive Canvas UI, and reproducible unit tests as the project’s canonical demo.
• Keep the experience dependency-free and procedural (no external generated bitmaps) so it runs from any local HTTP server and is testable in Node.

Description

• Added a minimal static server and npm scripts with server.js and package.json to serve the game locally and run tests.
• Implemented the playable app and UI in index.html, styles.css, and src/app.js, and moved deterministic game rules into src/game-core.js for testability (movement, targeting, waves, scoring, shrine health, and recovery).
• Added PLAN.md and an implementation log at .logs/2026-08-04-implementation.md, updated README.md with run/test instructions, and committed the full feature set.
• Added unit tests in test/game-core.test.js covering wave scaling, movement normalization/clamping, targeting range, shrine damage/game-over, and wave completion healing.

Testing

• Ran unit tests with npm test (node --test) and all 5 tests passed.
• Performed syntax checks with node --check src/app.js and node --check server.js, which succeeded.
• Started the server and ran HTTP smoke checks with curl http://localhost:4173/ and curl http://localhost:4173/src/app.js, which returned the expected pages.
• Ran repository checks (git diff --check / git status) which reported no problems, and the implementation was committed.
• Attempted to run the Codex manual helper node /opt/codex/skills/.system/openai-docs/scripts/fetch-codex-manual.mjs, which failed due to a network/DNS error (EAI_AGAIN developers.openai.com).

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Codex Task