docs: clarify TIME and SECOND wording

[JOY (JOY)]

Summary

• Clarify the canonical TIME / SECOND wording across project context and design docs.
• Define TIME as visible body-life state and SECOND as the earn, spend, loot, transfer, and ledger unit.
• Add UI examples for duration HUD, reward toast, bridge copy, shop pricing, and NPC dialogue.

Verification

• npx --yes markdownlint-cli2 README.md ROADMAP.md CHANGELOG.md CONTRIBUTING.md SECURITY.md AGENTS.md .claude/CLAUDE.md "docs/**/*.md"
• git diff --check
• markdown diff em-dash/en-dash scan
• AGENTS.md and .claude/CLAUDE.md sister-file comparison after header
• local code-review fallback: APPROVED, docs-only terminology alignment