Stabilize coordinated runtimes for beta66

[callumalpass]

Summary

• synchronously deactivate a collection watcher before registry removal, restoring active state if refresh fails
• own at most one abortable background mirror worker per replica and cancel it when the replica is no longer actionable
• retry transient or authorization object-part upload rejection with a fresh presigned URL for the same idempotent part number
• replace opaque upload-progress failures with privacy-safe state/count diagnostics
• pin merged mdbase-rs provider commit 818866705dcc4b6dcfd3bbc1ba63f83fdaec406f, which bounds watcher churn and keeps observation side-effect-free
• prepare the immutable 0.1.0-beta.66 staging candidate

Production remains on beta55; this candidate is for staging validation only.

Local validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace
• pnpm version:check v0.1.0-beta.66
• pnpm check:release-readiness
• pnpm check:architecture
• pnpm typecheck
• pnpm test
• pnpm e2e

Provider-specific validation includes the complete all-features/conformance suite, 25 consecutive parallel library runs after reproducing and fixing a watcher/settlement ownership race, and green Linux/macOS/Windows CI.