feat: add support exchange retrieval

[igorrendulic]

Summary

Telegram support search can now return Support Exchange evidence instead of collapsing nearby multi-author chat into one raw message result. Indexing derives requester/operator/peer/unanswered exchange records from source Telegram messages, keeps raw message evidence intact, and exposes authority labels so draft context can use prior operator answers without treating peer replies as support truth.

What changed

• Support profiles can store configured operator identities, which are used to label authoritative exchange responses.
• index now rebuilds Support Exchanges, chunks them as exchange documents, and includes exchange counts in CLI output.
• Search and draft context preserve requester/operator/peer roles, boost operator-answered exchanges, and surface sufficiency reasons for peer-only, ambiguous, or unanswered exchanges.
• Codex, Claude, setup docs, and workflow references now tell agent surfaces to present exchange roles instead of inferring authority themselves.

Validation

• uv run pytest passed: 172 tests.
• uv run ruff check could not run because ruff is not installed in the current environment; uv run --extra dev ruff check also failed to spawn ruff.

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