v0.5.0 — X/Twitter integration

X/Twitter integration

Adds X/Twitter as a source alongside WhatsApp/LinkedIn — mentions, DMs, posting,
and replying — via X's own official CLI/OAuth2 MCP bridge (xurl),
not a cookie/session-scraping library. Every unofficial alternative surveyed
carries real, maintainer-acknowledged account-ban risk, which isn't a trade
worth making on a real personal account.

• New: x MCP entry in .mcp.json.example (npx launcher,
  no local build required).
• New: docs/mcps.md setup section — Pay-per-use enrollment,
  the "Read and write and Direct Messages" app-permission gotcha (the default
  tier silently blocks DM scopes), OAuth2 callback config, and the credits
  requirement (auth can succeed while calls still 402 until the app is funded).
• X/Twitter wired in as a social source in both the
  briefing and dream
  routines' SOURCES config, same agnostic pattern as every other connector —
  no hardcoded account, so any Tars instance can plug in its own.
• Known limit: official DM reads are capped at 15 requests/15min,
  user-context OAuth only — no bulk/app-only tier. Routines should poll with
  that ceiling in mind.

Docs/config-only release — no code or schema changes.