Close phase 6 in the roadmap and open phase 7

[rohan-hotdata]

This PR closes phase 6 in the roadmap and opens phase 7 as issue #19. It changes docs/internal/roadmap.md and docs/internal/plan.md only.

How

• roadmap.md: phase 6 is closed with PR Phase 6: the accuracy loop, with sample B and the diagnosis split #18, and phase 7 is open with issue Phase 7: the extractor #19. Phase 6 gets its closing paragraph, with what it changed for later phases.
• plan.md: the phase 6 section is removed, because the plan keeps only the open phases. Its full text and decisions stay at commit 8a7318d.
• plan.md: the start table gains the sample B baseline and the split of the recalled group.
• plan.md: phase 7 names the target on both samples (19 on A, 16 on B), and lists the commands that phase 6 built.
• plan.md: task 2 of phase 7 gains a note, read from the code and not observed. A reply at the token limit is not stored in the cache. A reply that fails to parse is stored, but it stops the run, so no completed result file holds either fault.

Verification

• make verify passes, with the link check.
• A search of the diff and of issue Phase 7: the extractor #19 for private names found none.

Notes

• The untracked docs/internal/mem0-survey.md is not part of this PR.

[claude]

nit: The note says the cache does not hold a reply that fails to parse. The cache does hold that reply (not blocking).

Fix: "a reply that fails to parse is stored in the cache, but it stops the run. So no completed result file holds either fault, and this task confirms it."

CachedModels.__call__ stores each reply at bench/models.py:76-80 before it returns the reply. json.loads runs later, at bench/e2e.py:160, so a parse failure raises only after the insert. The token-limit case at bench/models.py:137-138 raises inside complete, so the first half of the note is correct. Without the fix, task 2 can look for the wrong thing in the cache.