docs: release notes for 0.16.0 (#122)

Adds the missing \`RELEASE-NOTES/0.16.0.md\` — the load-bearing notes
file the \`Release\` workflow needs to publish 0.16.0.

The 0.16.0 bump PR (#121) landed without it, so \`release-detection.ts\`
classified the merge as "not a release" and the \`release\` job skipped
(no npm publish, no GitHub Release). With this file on \`main\`, a
\`workflow_dispatch\` of \`release.yml\` with \`force: true\` will
complete the release (the \`commy-v0.16.0\` tag already exists and the
tag step is idempotent).

Author: GraemeF

RELEASE-NOTES/0.16.0.md

@@ -0,0 +1,37 @@
+Minor release of the commy plugin, **0.15.0 → 0.16.0**.
+
+## Highlights
+
+**Agents can now resolve and unresolve threads.** Two new MCP tools —
+`resolve_thread` and `unresolve_thread` — let an agent mark a topic resolved
+(Zulip's ✔ prefix) or clear that mark. Resolving a thread is the substrate's
+signal that a line of work is closed: a concierge draining a queue, a worker
+finishing a bead, or a human wrapping a discussion can now flip the topic's
+state in-band instead of leaving it ambiguously open. Unresolve reopens it when
+the work turns out not to be done.
+
+**Message and thread permalinks now point at the right granularity.** A
+message permalink resolves to the specific message (near/id narrow), while a
+thread permalink resolves to the whole topic (with narrow). Links you hand out
+now land where the name promises — a message link on the message, a thread link
+on the conversation — rather than both collapsing to the same narrow.
+
+## Fixes
+
+**Subscriptions restore even when the session id arrives late.** Building on the
+session-resume persistence added in 0.15.0: when the session id becomes known
+only after boot, the agent now restores its persisted subscription set reactively
+at that point, closing the window where a resumed session could briefly run with
+the wrong narrow set.
+
+## Maintenance
+
+- Message, channel, and thread observations are now branded Schemas with
+  permalink brands, tightening the port contract (internal; no behaviour change).
+
+---
+
+**Upgrading:** no action required. The new tools appear automatically; existing
+agents see no behaviour change until they call them.
+
+Seven-way version parity bumped in lockstep (enforced by `manifests.test.ts`).