docs(releases): 0.10.4 release notes (patch — internal refactors + PyPI metadata)

[lesnik512]

Summary

Release notes for 0.10.4 — a patch release. Every installed-package change since 0.10.3 is an internal refactor (no behavior change); the one user-visible change is richer PyPI metadata.

Per planning/releases/README.md, this PR is step 1 (write the notes, get reviewed). Tagging + the GitHub release (which triggers the PyPI publish) is the gated step 2, done only on an explicit go after this merges.

What's in 0.10.4

• refactor: dedupe outbox rules between real and fake clients #109 — outbox rules de-duplicated between the real and fake clients (_scheduling.py, _DLQ_PROJECTION) + a cross-adapter client contract suite. No behavior change.
• refactor(subscriber): give lease-lost telemetry one home #110 — lease-lost telemetry consolidated into one _emit_lease_lost helper. No behavior change.
• refactor(subscriber): make OutboxSubscriberConfig validate itself #111 — OutboxSubscriberConfig validates itself in __post_init__; behavior preserved exactly. No behavior change.
• chore: enrich PyPI metadata (keywords, classifiers, project urls) #108 — richer PyPI metadata (keywords, classifiers, project URLs). No runtime effect.

(#112, the planning decision-records convention, is not in the installed package, so it's excluded from the package-facing notes.)

Migration

None — drop-in from 0.10.x. No public-API, schema, or config change.

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