Add accessible live resource tooltips

[ael-dev3]

Summary

Adds concise, truthful explanations to the live Alpha 0.3.8 resource rail:

• Food, Wood, Stone, and Gold explain private keep balances, terrain-derived yield, completed ten-minute server cycles, and Collect settlement.
• Each resource explicitly distinguishes its live behavior from draft-only farms, logging, quarries, construction, mines, wagon expeditions, and spending.
• Community Marks is described as a separate community-attribution balance with no live spending, conversion, transfer, redemption, or reward loop.
• Tooltips support mouse hover, keyboard focus/Escape, click/touch activation, and outside dismissal.
• The open rail creates a continuous pointer corridor from both edge triggers into the tooltip, while the closed transparent rail still passes map input through.
• Stable descriptions and accessible trigger names are present before focus.

Scope

Based on protected main at f103514 (live Alpha 0.3.8).

This PR changes only:

• src/components/realm/RealmHud.tsx
• src/components/realm/RealmPlayerChrome.css
• tests/realmHud.test.tsx
• tests/realmCastleCssContract.test.ts

No candidate PR code was merged or copied. No SpacetimeDB/schema, auth, asset, gameplay-loop, release/version, documentation, deployment, or production-data change is included. Draft systems are mentioned only to say they are not live.

Verification

• npm test: 146 files / 1,483 tests passed
• npm run build: passed, including typecheck, runtime-asset checks, candidate-asset verification, production build, and production QA exclusions
• npm run verify:file-sizes: passed
• git diff --check origin/main...HEAD: passed
• Rendered local WebGL QA at 1280×720 and 360×800:
  • exactly one tooltip visible
  • all five explanations verified
  • no horizontal overflow
  • first and last desktop triggers fully overlap their tooltip corridor
  • mobile tooltip contained within viewport
  • Escape dismissal retained focus
  • no browser warnings or errors

Draft only. Do not merge until reviewed.

[ael-dev3]

Superseded by the audited Alpha 0.3.11 integration in #64, now merged to protected main. Accepted work was reconciled, corrected where needed, and validated there; this original branch is intentionally not merged again.