chore(release): v5.9.0 pins + changelog (gh-#777)

[genwave-radio]

🏷️ v5.9.0 pins + CHANGELOG (T508 · STORY-450 AC1 · gh-#777)

The pins PR for v5.9.0 — the first release its own gate proves. Merging this moves appliances on ./launch.sh --pinned to the v5.9.0 images once the tag exists; the tag itself is a separate step.

What changes

• compose.pinned.yaml: the five image pins home-v5.8.3 → home-v5.9.0 (admin_ui, engine, piper, icecast, api).
• CHANGELOG.md: one v5.9.0 entry covering PR-1…PR-11 (test(fixtures): one shared gw-test docker network for fixture compose (gh-#649) #785–ops(gate): the upgrade leg + role boundary (STORY-446, gh-#777) #790, ops(gate): the chaos legs — api-down and engine-reconnect (STORY-447, gh-#777) #792, ci(nightly): integration tier, chaos legs, one nightly-red issue (STORY-449, gh-#777) #793, ops(gate): T498 bound the api-down silence by total seconds (gh-#777, gh-#791) #798–test(specs): every skip says why, and the obsolete ones are gone (gh-#777, STORY-443) #802): test tiers, the shared test network (Test fixtures exhaust Docker's default address pools under a full-suite run #649), temp-dir cleanup (test: wizard/preflight specs leak temp dirs under /tmp (Story342–346, gh332, pawire) — ~60k dirs / ~500k inodes in a week #710), fake-clock budgets (test-flake: Story243 RendersRideThePerUnitBudget is still a wall-clock race (Orchestration FakeTimeProvider has no timers) — red on the js-yaml dependabot PR #716 #723), the stack gate (fresh, capture, upgrade, chaos), nightly.yml, release.yml gating promotion on the gate, the skip-prefix law, and the upgrade note.
• Abstractions unchanged: git diff v5.8.3..main --stat -- src/GenWave.Abstractions/ is empty; the only src/ change since v5.8.3 is AdScriptWriter.cs (fake-clock budget, behaviour unchanged on a real clock).

Evidence

• tools/check-doc-drift.sh → exit 0 ("pins: all compose.pinned.yaml images pinned to home-v5.9.0").
• Full solution (Category!=Integration): 5266 passed / 15 skipped / 0 failed across the nine projects.
• Review: one round, PASS-WITH-NOTES (six wording corrections to the entry, applied: Tier 2 red: Story346 real-Postgres verify probe expects db/46's marker that the container never gets #796's real root cause, the tier-2 definition per CONTRIBUTING, the Story384 shape pins instead of a non-existent baseline diff, exact skip counts 433/436, rerun semantics, the report line's punctuation).

After merge (T509, Dean)

1. Push the v5.9.0 tag → release.yml runs build-test → build-images → merge-manifests → stack-gate → promote → create-release.
2. home-latest and the Release move only after stack-gate passes; the Release body carries "What this release proved".
3. Demo: git pull && ./launch.sh --pinned, then the listening check.
4. Close gh-/design seed: integration + captured-audio CI gates (nightly and release) #777, Test fixtures exhaust Docker's default address pools under a full-suite run #649, test: wizard/preflight specs leak temp dirs under /tmp (Story342–346, gh332, pawire) — ~60k dirs / ~500k inodes in a week #710, test-flake: Story243 RendersRideThePerUnitBudget is still a wall-clock race (Orchestration FakeTimeProvider has no timers) — red on the js-yaml dependabot PR #716 #723 (and /explore seed: sponsors — the customer behind every ad, and a guided spot dialog #714, /explore seed: jingle packs + voice packs — two catalog kinds (Kokoro voice-designer .pt voices; instrumentals and jingles) feeding #708 beds and #702 casts #709, feat(epic): parody advertisements — LLM-authored joke ads with a pre-rendered Ads library #380) with the run link.

Nothing is tagged or merged by this PR.