chore(p0): remove the improve lever and the plane improvement loop

Off every active line (PATHFINDER-2026-10-13/03-unified-proposal.md, cuts).
Deleted: src/openultrasast/improve/ (1,175 lines), the ousast improve
subcommand, plane/tasks/loop.py and loop.yaml with the --loop generation,
the memory-snapshot step in memory.seed, pairs.build_pair_signals, and the
four improve tests plus the loop cases in other tests. Docs no longer
describe the lever. Net: 3,073 lines deleted, 83 added. Targeted tests:
154 passed; 3,436 tests collect.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

README.md

@@ -217,8 +217,7 @@ checks, plus a configuration census. A model answers only the residual question.
   code it comes from and what it misses.
 - [docs/architecture.md](docs/architecture.md) gives the stage order and the evidence ladder (a
   state machine, not a label a model may assign). It also covers the central CWE policy, the
-  project score and the self-improving loops (`ousast improve`, with `--memory` for proposals from
-  plane rows).
+  project score.
 
 Quick rules cover C/C++, Python, JavaScript/TypeScript, Java with Groovy templates, and PHP. Each
 rule runs only against files of its language.
@@ -311,7 +310,6 @@ the fold discipline that keeps learned decisions out of their own training data.
 uv run ousast benchmark benchmarks/manifests/python-vulnerable.toml --mode quick
 uv run ousast pairs --slice sast                     # fire on the vulnerable side, stay silent on the fix
 uv run python -m openultrasast.pair_gate             # CI: local pairs must all pass
-uv run ousast improve benchmarks/manifests/java-spring-boot-vulnerable.toml --dry-run --memory
 ```
 
 ## Token economics