Fix stale-post refresh for DMs

[wca4a]

What changed

• Restrict stale-post refresh requests to group channel nests.
• Keep DM and group-DM conversations on their existing subscription and sync paths.
• Catch changed-post refresh failures, clear pending IDs, and allow a later retry instead of producing an unhandled promise rejection.
• Add regression coverage for group channels, DMs, and group DMs.

Why

useRefreshPosts called syncUpdatedPosts for every conversation type. That reaches getChangedPosts, whose server endpoint is explicitly implemented only for group channels. Opening a DM with stale posts could therefore throw server does not implement this endpoint for non-group channels as an unhandled promise rejection and show the React Native error screen.

Impact

DMs no longer call an unsupported group-channel endpoint. Group-channel stale-post refresh remains unchanged, aside from handling transient failures cleanly and permitting retries.

Validation

• pnpm --filter @tloncorp/shared exec vitest run src/store/useChannelPosts/queries.test.ts — 12 tests passed
• pnpm --filter @tloncorp/shared exec tsc --noEmit — passed
• Targeted ESLint — no new errors; two pre-existing queryRef dependency warnings remain
• Reproduced in the iOS Simulator with ~pinser-botter-podfyl-parseb, reloaded with the fix, then reopened the exact DM without a new console error

[wca4a]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

Reviewed commit: 4949a8e728

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