[G3] Retire duplicated harness knowledge: docs, sibling-repo runbooks, burn collector transfer, and the "one owner" guardrail test #184

Part of #160 (group 3 — depends on #183 parity report; parallel with burn #562 cutover).

Scope

1. This repo's docs: README.md ("Why ai-hist" → add "the sourcing layer for burn"), docs/architecture.md (consumer diagram gains burn (cost) beside CLI/MCP), docs/session-catalog.md (per-source matrix is now the contract of record; link the ADR [G1] ADR: relayhistory owns session sourcing; burn consumes evidence through a Rust SDK #161), docs/product-direction-style pointers in AGENTS.md. Remove any statement that another repo parses harness logs.
2. Sibling repos (separate PRs, linked here):
   • AgentWorkforce/relayhistory-cloud docs/agent-runbook.md §Pair: replace "Burn remains the source for cost/usage/tool dimensions; relayhistory/ai-hist remains the source for recall/trajectory-derived decisions" with "relayhistory owns session capture (usage, tools, files, topology); burn owns pricing and cost and reads relayhistory" and docs/product-direction.md §2 convergence map rows for ../burn and ../ai-hist.
   • AgentWorkforce/burn README.md first paragraph ("Burn ingests Claude Code, Codex, and OpenCode session logs…") → "Burn reads sessions from relayhistory and prices them" (done in burn #562; verify here).
3. Collector transfer close-out: for each burn collector issue mirrored by [G1] One-entry harness registry and out-of-tree local source plugins (absorb burn's collector backlog) #177, confirm the relayhistory issue exists, then close the burn issue as not_planned with a pointer (burn #560 does the burn-side comment; this issue verifies none were missed).
4. Guardrail: a CI test in this repo that fails if AgentWorkforce/burn main's crates/relayburn-sdk/src/ contains a reader/claude.rs, reader/codex.rs, or reader/opencode.rs after burn's cutover release tag — a cheap "second parser reappeared" tripwire (script: shallow-clone burn, test ! -e), scheduled weekly, not on PRs.
5. CHANGELOG.md entry summarizing the epic outcome for users: what burn users should expect (one ingest, ai-hist database is now the source of truth for both tools).

Acceptance

• No doc in this repo, relayhistory-cloud, or burn describes burn as a log parser.
• All 19 burn collector issues closed with pointers; 19 relayhistory collector issues open.
• Tripwire workflow green on the week after burn's cutover release.

Out of scope

Anything code-side in burn.