chore: prepare public release hygiene and messaging

[kwalus]

Summary

• remove a local-only MCP launcher from the public tree
• tighten ignore rules so local-only helper scripts are less likely to leak into the public repo
• replace the stale release-announcement draft with a reusable public-safe template

Why

• public repo content should stay free of machine-local helpers and private-testing language
• this prepares the follow-on public trust/governance PR so it can describe expanded trust controls and operator workflows without implying there was no trust surface before
• this PR is hygiene and messaging prep only; it does not yet carry the runtime trust-control changes themselves

Test plan

• verified the cleaned files no longer reference private repo names or local service endpoints
• verified the launcher is removed from the tracked tree and ignored going forward