chore: standardize public identity and release promotion

[stefan-jansen]

Outcome

• aligns package, repository, and README identity with canonical ML4T metadata
• executes the credential-free README quick start from the installed wheel and checks documentation links
• records version and commit identity in rendered documentation
• replaces main-push documentation deployment with a protected, commit-bound release promotion
• validates an explicit unpublished main candidate, writes a digest manifest, publishes one qualified build, and post-verifies PyPI, GitHub, and deployed docs
• removes copied issue-template scope, private-sidecar discovery, stale public plans, drafting residue, and obsolete nested agent indexes
• stabilizes the callback-timeout recovery test while preserving its behavioral contract

Compatibility

No runtime API or serialized format changes.

Verification

• full stable gate: 1,028 passed, 29 skipped, 85.83% branch coverage
• stress and sustained performance qualification passed
• five critical-fault repetitions passed
• strict MkDocs build and rendered identity passed
• reproducible wheel/sdist, six clean install profiles, README quick start, and security qualification passed
• all 75 documentation links, including 17 unique external targets, passed
• actionlint and ecosystem workspace audit passed
• callback-timeout recovery passed 10 independent repetitions and the complete engine unit module passed with 51 tests

Closes #79

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