feat(conventions): generalize defaults, backfill old projects, adopt the standard in-repo

Harden the architectural-conventions standard so it works out-of-the-box on
any project and resolves for projects that predate it, and make RoboCo pass
its own gate.

General defaults (apply to every project, not just one with a tuned file):
- The auto-scan excludes test and documentation trees (tests/, docs/) — those
  legitimately define fixtures and aren't enforced code.
- Helper placement seeds at warn, not block: `helper` matches any top-level
  function, too blunt a signal to hard-block a route file's small private glue.
  Misplaced model/route/component stay block; the body-level thin_routes check
  remains the real fat-handler guard.
- thin_routes no longer counts transaction-lifecycle calls (commit/flush/
  refresh) as data access — an explicit `db.commit()` after delegating to a
  service is a valid pattern.
- no_lint_suppressions exempts a small allowlist of structurally-unavoidable
  framework codes (ruff TC001-TC003, pydantic prop-decorator); bare or other
  suppressions still flag.
- CLAUDE.md rule-lifting skips bare common-word tokens that would match
  everywhere (e.g. "commit"), keeping only specific identifiers.
- The ambient prompt block lists only constrained modules and truncates at a
  line boundary with a "+N more" pointer instead of cutting mid-line.

Backfill: the standard previously read the committed file + repo scan from
project.workspace_path, a field only a manual API call set — so an older
project (or one whose workspace was cleared) showed an empty "missing" map no
matter what was pushed. The service now ensures a dedicated, default-branch
read clone on demand (WorkspaceService.ensure_read_clone) and resolves from
it, persisting the resolved path + real HEAD. The panel tab, the spawn-time
ambient block, and the per-task constraints all resolve the committed standard
with no manual setup.

Adopt in-repo: relocate the inline request/response models from the system and
*_live route modules into roboco/api/schemas/ so the codebase passes its own
placement gate, and ship a canonical .roboco/conventions.yml. no_models_in_routes
and modular_cohesion are now clean and enforced at block.

Docs updated across the user guide, the agent-facing RAG standard, the
developer and pr_reviewer role prompts, CLAUDE.md, and the changelog. New unit
tests cover the scan exclusions, helper-warn, the suppression allowlist, the
commit exemption, and the resolve/backfill path; the conventions + project
integration suites pass against Postgres.

roboco/api/routes/project.py

@@ -473,8 +473,12 @@ async def get_conventions(
     """Return the project's effective conventions map + its current health."""
     project = await _get_project_or_404(get_project_service(db), project_id)
     conv = get_conventions_service(db)
-    standard = await conv.get_map(project)
-    health = await conv.health(project)
+    # Ensure a default-branch read clone once, then read the map + health from
+    # it. This is the backfill: a project created before the standard existed
+    # (no manual workspace_path) still resolves its committed conventions file.
+    workspace = await conv.resolve_workspace(project)
+    standard = await conv.get_map(project, workspace=workspace)
+    health = await conv.health(project, workspace=workspace)
     await db.commit()
     return ConventionsResponse(
         standard=standard.model_dump(mode="json"),