docs: add public contributor development skills

[hetaoBackend]

Change

Add five discoverable contributor skills under .agents/skills: CLI navigation, cross-layer drift checks, test selection, runtime consumer verification, and retrospectives. Adapt the workflows from the shared source repository to this distribution's TUI/exec/ACP paths, public boundaries, English documentation, and declared verification gates.

Add contributor links and regenerate the reviewed public file inventory. Product runtime skills and runtime code are unchanged.

Validation

• Revision: f6c85800033e077f37b367687036b28284e2c348.
• All five skill schemas and local references: PASS.
• git diff --check: PASS.
• Gitleaks full local Git history: PASS, no leaks found.
• pnpm verify (full profile, darwin/arm64, Node v26.4.0): PASS, all 14 gates. Capability suite: 132 files / 3,377 tests passed. The release-tool suite's Windows-only test is intentionally skipped on macOS.
• NOT RUN: Linux/Windows local validation and live-provider/service acceptance. No runtime behavior was changed.

Publication and contribution checks

• I have permission to contribute these changes under the existing licenses applicable to the changed files/packages; imported material and its provenance are identified and existing notices are preserved.
• No credentials, account data, real user content, internal source history or private review material is included.
• Added/removed source files were reviewed before regenerating release/public-source.json; no new tests were added.
• Contributor documentation is updated; shared README content is unchanged. Offline checks are not represented as live-service acceptance.

Maintainer handoff

Publication scope: five reviewed contributor-skill files added to the inventory. No license changes.

Shared-source port: not needed for this standalone contributor-workflow adaptation. No source baseline advancement or internal history import is included.

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