FN-8404: extract dashboard domain route registrars

Move maintenance, AI text assistant, and setup/activity endpoints into focused dashboard route registrars.

- Register the extracted domains in the API mount sequence.
- Preserve route precedence and document registrar responsibilities.
- Add registrar coverage and refresh the modular-route baseline.

Files changed:
 packages/dashboard/src/routes.ts                   | 948 +--------------------
 packages/dashboard/src/routes/README.md            |  82 +-
 .../register-ai-text-assistant-routes.test.ts      |  49 ++
 .../register-setup-activity-routes.test.ts         |  54 ++
 .../register-system-maintenance-routes.test.ts     |  48 ++
 .../src/routes/create-api-routes-mount-sequence.ts |   8 +-
 .../routes/register-ai-text-assistant-routes.ts    | 327 +++++++
 .../src/routes/register-setup-activity-routes.ts   | 320 +++++++
 .../routes/register-system-maintenance-routes.ts   | 320 +++++++
 scripts/lib/routes-modular-baseline.json           |   2 +-
 10 files changed, 1176 insertions(+), 982 deletions(-)

Fusion-Task-Id: FN-8404

Fusion-Task-Lineage: d6b5be1f-e011-47fc-a7f8-5df89893766f

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

scripts/lib/routes-modular-baseline.json

@@ -1,3 +1,3 @@
 {
-  "inlineRouteRegistrations": 42
+  "inlineRouteRegistrations": 23
 }