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

[Copilot]

Multiple open PRs have accumulated actionable but unimplemented review feedback. This PR addresses all unresolved comments in a single changeset to unblock clearing the backlog.

API robustness (src/services/xapi.ts)

• URLSearchParams for mentions endpoint — replaces fragile string concatenation, adds since_id support when lastMentionId is set
• Array.isArray guard before parseThread — prevents crash when API returns non-array data
• Typed parseThread parameter — any[] → { created_at: string; [key: string]: unknown }[]

// 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);

Type safety (src/services/grok.ts)

• Replace const data: any with unknown + runtime structure validation before narrowing to typed access

Workflow fix (auto-label.yml)

• Remove duplicate with: key — this was a YAML parse error causing the auto-label workflow to fail on every trigger

Docs (README.md)

• Fix & → and for readability
• Fix broken ordered list (. Visit → 1. Visit)

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