chore(release): prepare v0.7.0 — changelog, version bump, docs

[ajianaz]

Summary

Release preparation for v0.7.0 — consolidates the [Unreleased] entries accumulated since v0.6.2 into a versioned release section and updates the related documentation. No behavior change (docs + version only).

Why 0.7.0 (minor)

Since v0.6.2 the release adds a new feature (inbound caller / blast-radius context resolution) and deny_unknown_fields is a breaking-minor change for configs that previously relied on silently-ignored typos. Semver minor → 0.7.0.

Changes

• Cargo.toml / Cargo.lock: 0.6.2 → 0.7.0.
• CHANGELOG.md: reorganized into Highlights + Added / Changed / Fixed under a ## [0.7.0] - 2026-07-16 header, with a fresh empty [Unreleased] on top.
• docs/changelog.md: matching concise release notes.
• docs/configuration.md:
  • New "Cross-File Review Context" section documenting review.context_chain (enabled, max_context_tokens=5000, follow_depth, include_tests, include_callers), the outbound/inbound axes, and the signature-only budget fallback.
  • Config Resolution Order: notes that values are validated at load time and typos rejected via deny_unknown_fields.
  • Quality Gate: notes CategoryAction is a case-insensitive validated enum and a disabled gate never fails.

Validation

• All 659 tests pass.
• Clippy clean, fmt clean.
• Changelog verified free of nested-backtick rendering issues.

This PR lands the prep on develop. The actual release still requires a develop → main PR + v0.7.0 tag on main (which triggers the publish workflow) — to be done separately with explicit go-ahead.