docs: add stability policy (STABILITY.md) and link it across contributor docs

[leostar0412]

Summary

• Adds STABILITY.md, defining Tier A (stable), Tier B (evolving), and Tier C (unstable) interfaces for operators and contributors.
• Documents semver/release expectations for 0.x tags on main, including scheduled commands, /health/, env vars, schedule YAML, core public API, and cross-app sync_api exports.
• Links the policy from README.md, CONTRIBUTING.md, docs/README.md, docs/Onboarding.md, and docs/Core_public_API.md.
• Adds a short stability note to github_activity_tracker/sync_api.py and cppa_pinecone_sync/sync_api.py module docstrings.
• Records the addition in CHANGELOG.md under [Unreleased].

Apps touched

• docs (root + docs/)
• github_activity_tracker (docstring only)
• cppa_pinecone_sync (docstring only)

Test plan

• Documentation-only change; no runtime behavior changed
• python -m pytest (or scoped: python -m pytest <app>/tests) — N/A
• uv run pyright (if typed code changed) — N/A
• lint-imports (if imports or cross-app coupling changed) — N/A
• App command smoke-tested (if collector/command changed) — N/A

Docs / coupling

• App README or docs/ updated (if behavior or ops changed)
• cross-app-dependencies.md updated (if FKs or cross-app imports changed) — N/A
• python scripts/generate_service_docs.py run (if services.py or core/protocols.py changed) — N/A

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Closes #237

Summary by CodeRabbit

• Documentation
  • Added a formal Stability policy describing Tier A/B/C interfaces, versioning, deprecation, and deployment rules.
  • Added a Stability section to the README and linked the policy from contributing, changelog, onboarding, docs index, and module docs.
  • Clarified stable contracts for the health endpoint, scheduled commands, and allowed cross-app imports; moved the related changelog entry into Unreleased.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 78a3ae3a-cc1f-4cb4-8367-6094875e8e3c

📥 Commits

Reviewing files that changed from the base of the PR and between b7bea06 and 7ff5d38.

📒 Files selected for processing (3)

• README.md
• STABILITY.md
• docs/cross-app-dependencies.md

✅ Files skipped from review due to trivial changes (2)

• docs/cross-app-dependencies.md
• README.md

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📝 Walkthrough

Walkthrough

Adds a STABILITY.md stability policy and wires references into README, CONTRIBUTING, CHANGELOG, module docstrings, and docs to declare Tier A/B/C interface guarantees and related release/deprecation rules for v0.x.

Changes

Stability Policy Documentation for Production v0.x

Layer / File(s)	Summary
Core stability policy document STABILITY.md	Defines interface stability tiers (Tier A/B/C), SemVer and main-tag deployment rules for v0.x, and concrete Tier A contracts (GET /health/, scheduled management commands, environment variable names, schedule YAML shape, and allowed cross-app sync_api exports), plus deprecation and deployment guidance.
README and contributor stability guidance README.md, CONTRIBUTING.md	README adds a "Stability" section describing the 0.x production contract and links to STABILITY.md. CONTRIBUTING.md adds a guideline requiring updates to STABILITY.md and CHANGELOG.md when sync_api.__all__, /health/ JSON contract, or scheduled management command names change; branching strategy bullets updated.
Changelog entry and module docstring updates CHANGELOG.md, cppa_pinecone_sync/sync_api.py, github_activity_tracker/sync_api.py	CHANGELOG.md records the new STABILITY.md in Unreleased and moves the Pydantic boundary schemas bullet into Unreleased. Both sync_api module docstrings add notes that Tier A symbols are the ones listed in __all__ and reference STABILITY.md.
Documentation index and guide links docs/Core_public_API.md, docs/Onboarding.md, docs/README.md, docs/cross-app-dependencies.md	Core_public_API.md states that stability guarantees for listed core imports are governed by STABILITY.md Tier A. Onboarding.md, docs/README.md, and cross-app-dependencies.md add links/index entries pointing to STABILITY.md.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Suggested reviewers

• wpak-ai
• snowfox1003
• jonathanMLDev

Poem

🐰 I wrote a note for steady days,
Tiers to guide our code's highways.
Tier A stays steady, Tier C can roam,
Docs linked and filed to find a home.
Hop on — the policy finds its place.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: adding a stability policy document and linking it across documentation.
Description check	✅ Passed	The description covers all required sections: summary of changes, apps touched, and test plan with appropriate checkboxes marked.
Linked Issues check	✅ Passed	The PR fully addresses issue #237 by adding STABILITY.md with Tier A/B/C interface definitions and documenting stable vs unstable interfaces.
Out of Scope Changes check	✅ Passed	All changes are in-scope: documentation and module docstrings only, no runtime behavior changes or unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[leostar0412]

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Actionable comments posted: 0

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