docs: rewrite README to house standard

[steipete]

Summary

Rewrites the README to the shared house structure: a one-line pitch and dynamic badge row, npm-first installation, a credential-free 60-second mapping path, the provider-backed review path, progressively deeper workflow sections, development commands, and license.

The README is now 103 lines instead of 230. The existing banner remains near the top.

Content movement

No new docs were needed. The removed exhaustive material already lives in the focused guides:

• mapper coverage and gaps: docs/feature-mapping.md
• provider setup and permission boundaries: docs/providers.md
• command workflows and flags: docs/quickstart.md, docs/code-review.md, docs/patching.md, docs/reporting.md, and docs/validation.md
• configuration and safety: docs/configuration.md and docs/safety.md

Dropped as obsolete: the "early CLI" status, the "next steps"/coming-soon mapper sentence, and the stale claim that a future v0.4 would remove legacy report JSON keys (the project is now v0.7.x). No factual feature coverage was discarded.

Verification

• Confirmed the repository is public and active; default branch is main; primary workflow is .github/workflows/ci.yml.
• Confirmed clawpatch is published on npm (npm view clawpatch version returned 0.7.2), Node >=22 is declared, both pnpm and npm global install paths succeed, and neither checked Homebrew tap contains a formula or cask.
• Built the current worktree and ran the README quickstart against a temporary Git repository: init, map, status, and report succeeded; mapping found four features without calling a provider.
• Validated provider-dependent doctor and review commands, plus all workflow commands and documented flags, against the built CLI's real --help output. No model call was made because it requires provider credentials.
• No source code sample remains in the README, so there was no code snippet to typecheck separately.
• pnpm typecheck, pnpm lint, pnpm format:check, pnpm test, pnpm build, and pnpm pack:smoke passed (29 test files; 900 tests passed, 1 skipped).
• All 14 relative links resolve. All external URLs satisfy the HTTP check (npm's expected automated-client 403 accepted), and all four Shields URLs return valid, non-error SVGs.
• Required autoreview: clean, no accepted/actionable findings.