docs/AI_AGNOSTIC.md lists every place the forge names or assumes one AI vendor #12121

Done looks like:

• docs/AI_AGNOSTIC.md has a table of every place under src/ (and docs, scripts) that names or assumes a vendor: code seams, env names (FORGE_CLAUDE*, CLAUDE_CONFIG_DIR, ANTHROPIC_*), log lines ("crew is up claude=…"), page and TUI words, settings, prompts tuned to one model. Each row has a file, a line or symbol, and a mark: seam / word / tuning
• Each row names the issue from this plan that removes it
• Linked from docs/REFERENCE.md

No code changes. Files: docs/AI_AGNOSTIC.md, docs/REFERENCE.md

Part of the owner's ask #12068 (AI agnostic). Keep this pull to the files named; earlier tries went red by spreading into src/flow, src/core/events and src/boards. A new process start must be listed in test/spawn-sites.test.ts (and test/spawn-pipes.test.ts) with its reason. The branch mason/12068-the-forge-is-ai-agnostic-you-connect-you (f580581a93e3) holds earlier work to borrow from, not to merge whole.