fix: address design review ACT NOW items (6 risk gaps)

- Add migrate_config() to ConfigGenerator protocol for schema version upgrades
- Add per-server operation lock to ProcessManager to prevent start/stop races
- Add busy_timeout retry/backoff strategy (exponential: 1s, 2s, 4s) for DB lock exhaustion
- Add ConfigForm testing strategy and error boundary for malformed schemas
- Add schema cache invalidation on adapter version change
- Add ConfigMigrationError to typed adapter exceptions

IMPLEMENTATION_PLAN.md

@@ -447,6 +447,7 @@ Verify React app can:
 ### Adapter contract tests
 - Template test suite that any new adapter should pass
 - Tests: ConfigGenerator produces valid sections and valid config files, ProcessConfig returns allowed executables, LogParser parses sample lines
+- ConfigGenerator migration test: `migrate_config(old_version, config_json)` returns valid migrated dict; `ConfigMigrationError` on invalid old_version
 
 ### Load notes
 - SQLite with WAL handles concurrent reads from 4 threads per server well