fix: consolidate unresolved review feedback from PRs #26, #6, #4, #13

[Copilot]

Sweeps actionable, unresolved review comments across open PRs into a single mergeable change to unblock the backlog.

Type safety (xapi.ts, grok.ts)

• Replace string-concatenated mentions URL with URLSearchParams (includes conditional since_id)
• Add Array.isArray() guards before parseThread() and in searchTweets() — prevents runtime crash on unexpected API shapes
• parseThread param: any → unknown
• grok.ts: type the API response instead of any; as any → as AgentAction['type']

// Before
return this.parseThread(response.data || []);

// After
if (!Array.isArray(response.data)) {
  console.warn('Unexpected response shape from X API (thread): data is not an array');
  return null;
}
return this.parseThread(response.data);

Agent correctness (agent.ts)

• Process mentions oldest-first (X API returns newest-first) so Set insertion order matches chronological order for correct pruning
• Add bounded pruning with safe { value, done } iterator destructuring (cap: 1000)

GitHub Actions permissions

• auto-label.yml: pull-requests: write
• issue-triage.yml: issues: write
• pr-checks.yml: pull-requests: write, remove .py from node -c syntax check

Docs

• README.md: fix double-space typo, clean up wording

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[groupthinking]

Closing stale draft — superseded by cleanup/ready-to-use merge to main