Read-only host: flybot/* reads rejected, social timer ignores writer lock (PR #2 review) #14

Context

When Web and Desktop share a team, one host is read-only. That host currently fails every flybot/* endpoint, including reads, while the social timer still writes. Flagged in the PR #2 review (item 16) and in a Codex inline comment, and still present at 7b806c6.

Original feedback

• @hsliuustc0106 review (permalink), item 16: "the READS allowlist in src/host/channel.js excludes every flybot/* name … and the social timer path doesn't check the writer lock at all, so a read-only Web window still polls, registers and delivers."
• Codex inline comment, Allow read-only FlyBot query endpoints (permalink), ds-bot/src/host/channel.js L326 (P2).

Where (at 7b806c6)

• src/host/channel.js#L85 (READS), #L110 (read-only rejection), #L326 (flybot/ dispatch)
• the social polling and registration timers

Proposed fix

• Classify FlyBot query endpoints (flybot/bots, changes, approvals, social/remote-bots, …) as reads. Keep decisions and plugin mutations rejected.
• Gate the social poller, registration and delivery on holding the writer lock.

Acceptance criteria

• A read-only host renders the tree and social UI.
• A read-only host never calls list_inbox, add_home_member or delivery.
• Tests cover both cases.

Refs: PR #2 (merged), umbrella #3. Verified against Birfy/FlyBot flybot-plugins tip 7b806c6.