Fix stale docs and stop tracking ignored files

[chrishonson]

Summary

Two housekeeping commits found by a review of release.

Documentation that had drifted

• CLAUDE.md listed list_context twice in the MCP tools table. It is now one row.
• NEXT-STEPS.md still said to start CORE #70. PR Close memory lifecycle correctness gaps and record the foundation acceptance #14 landed it and production serves revision metacortexmcp-00031-dig, so the item now says so.
• AGENTS.md described three composite indexes. firestore.indexes.json defines eight, plus three TTL field overrides. The bullet now lists all of them.
• metacortexplan.md gets a dated CORE #70 acceptance record at the end of the file: the commits, the checks that passed, and the limitations (no post-deploy check against production is recorded, and VERIFY #69 is still open).

Files that were committed but should not be

• firestore-debug.log (an emulator log) is removed, and .gitignore now ignores *-debug.log.
• 36 files that .gitignore already excludes were still tracked: skills-lock.json and the agent skill files under .agent/ and .agents/. They are untracked with git rm --cached. They stay on disk in clones that already have them, but pulling this change removes them from a checkout where they were tracked. They can be regenerated from the lock file.

Left alone on purpose: slides.html and the 10 MB screen recording it embeds. Untracking the recording would not shrink history and would break the slides.

Docs and tracking only. No code, no deploy.

Test plan

• metacortex_typecheck passes
• metacortex_test passes: 11 files, 139 tests, 77.76% line coverage
• metacortex_package passes (Journey install, 70 files)
• CI on this PR

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