chore: align repository configuration comments

[Kevinjohn]

Closes #1470

Aligns comments in repository and deployment configuration with DEFENSIVE-CODING.md §7. Removes stale history and duplicate explanations while preserving current security, operator, and deployment guidance. The exact historical fixture exceptions in .gitleaks.toml remain documented.

Runtime configuration is unchanged.

Validation:

• Comment-style checker (passed)
• Prettier check for applicable files (passed)
• git diff --check (passed)
• Comment-only syntax comparison for changed source files (passed)
• Commit hook: Paraglide compilation and lint-staged ESLint (passed)
• Push hook: format, typecheck, lint, and file-size policy (passed)

No application test suites were run because this change only edits comments.

Merge predecessor: none.

Merge order

#1465, #1471, #1472 → #1473, #1474, #1466

• No textual conflicts with main (8141c39) or between any pair. All six merged in this order onto main cleanly, and the combined tree passes format, typecheck, lint, file-size and comment-voice checks, the docs build (tree clean) and the documentation suites.
• Rewrite the documentation front door around four role quick starts #1466 lands last because it carries regenerated docs/ output.

Merge predecessor for this PR: none.

Conflicts: none.

[Kevinjohn]

Polish review: no P1 or P2 findings, no changes pushed.

• Comment-only claim verified: every changed config file (.env.example, .gitattributes, .gitignore, .gitleaks.toml, .zap/rules.tsv, docker-compose.yml, security.yml, eslint.config.js, playwright.config.ts, vite.config.ts, public/theme-init.js) is identical once comment lines are removed; the TS/JS files also print identical comment-stripped ASTs. The only non-comment text change is the _comment value in stryker.config.json, which Stryker ignores.
• Ladder passed on Node 24 at the PR head: pnpm run check:push (format, typecheck, lint with zero warnings, file-size policy) and pnpm run policy:comment-voice.
• Integration: chore: align repository configuration comments #1471, chore: align server, shared, and script comments #1472, fix: surface unexpected repeat time-off failures #1473, chore: clarify E2E test comments #1474 and Rewrite the documentation front door around four role quick starts #1466 merged in that order onto main at 8141c39 without conflicts; check:push, policy:comment-voice, docs:build (tree clean afterwards) and the documentation, runbook and user-story suites (430 tests) pass on the combined tree.

Merge predecessor: none.