Add project governance charter

[Yuxin-Qiao]

Summary

• add a lightweight, public governance charter for contributors and maintainers
• document decision making, high-risk ownership, merge and release expectations, security handling, and maintainer continuity

Why

The project has contribution and security documentation in flight, but it needs a durable, discoverable statement of how responsibility and decisions work without depending on one person’s undocumented knowledge.

Linked issue / maintainer sign-off

No linked issue: governance baseline documentation.

Validation

• make check: passed
• make test: blocked by an unrelated baseline failure on main. SessionEquivalentForecastTests has four singular/plural expectation failures; this PR changes no executable code or test resources. The failing group was reproduced independently.

UI proof

Not applicable: documentation-only change.

Provider / privacy

• no provider code, credentials, data handling, or runtime behavior changed
• the charter records review expectations for credential- and provider-sensitive paths

[clawsweeper]

ClawSweeper status: review started.

I am starting a fresh review of this pull request: Add project governance charter This is item 1/1 in the current shard. Shard 0/1.

This placeholder means the worker is alive and reading the current context. I will edit this same comment with the actual review when the claws are done clicking.

Crustacean status: shell secured, claws on keyboard, evidence pebbles being sorted.

[steipete]

Thanks for the thoughtful work on this stack, @Yuxin-Qiao — the technical pieces (the test-baseline repair in #2418 and the CI hardening) are genuinely appreciated and are being handled on their own merits.

On the governance charter itself: CodexBar is a single-maintainer project and Peter has decided he doesn't want a formal governance document creating public process commitments here. Closing this one — no reflection on the quality of the writing.