chore(deps): unblock the ccxt/setuptools lock deadlock and cut dependabot churn

Dependabot could not land either half of a mutually-blocking pair: the
minor/patch group wanted ccxt 4.5.68 (which pins setuptools==83.0.0) while
keeping setuptools at 82.0.1, and the separate setuptools 83.0.0 PR conflicted
with the ccxt 4.5.67 already in the lock. Neither can go green alone because
setuptools is a major bump and is excluded from the minor/patch group by
design, so it cannot ride along.

Regenerate the lock so both move together. Verified with pip-compile under
Python 3.11 on Linux (matching CI) and checked with CI's own gate,
pip install --dry-run --require-hashes. Note the lock is platform-sensitive:
regenerating on macOS drops jeepney/secretstorage and swaps py-mini-racer for
mini-racer, so it must be produced on Linux.

Also ignore websockets, capped at <16 by langgraph-sdk 0.4.2, and move all
three ecosystems to monthly with 2 concurrent PRs. Security updates are a
separate channel and are unaffected.

.github/dependabot.yml

@@ -4,8 +4,8 @@ updates:
   - package-ecosystem: "pip"
     directory: "/"
     schedule:
-      interval: "weekly"
-    open-pull-requests-limit: 4
+      interval: "monthly"
+    open-pull-requests-limit: 2
     groups:
       # Minor/patch bumps are low-risk and reviewed as a single batch; majors
       # are excluded so they still arrive individually and get real scrutiny
@@ -26,13 +26,17 @@ updates:
       # PR failed CI with ResolutionImpossible. Drop this ignore once aiofile
       # ships a release that accepts caio 0.10.
       - dependency-name: "caio"
+      # websockets is likewise capped by our tree: langgraph-sdk 0.4.2 requires
+      # websockets<16, so a bump to 16.x is unresolvable. Drop this once
+      # langgraph-sdk widens its range.
+      - dependency-name: "websockets"
 
   # Frontend npm dependencies.
   - package-ecosystem: "npm"
     directory: "/frontend"
     schedule:
-      interval: "weekly"
-    open-pull-requests-limit: 4
+      interval: "monthly"
+    open-pull-requests-limit: 2
     groups:
       npm-minor-patch:
         applies-to: version-updates
@@ -52,8 +56,8 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "weekly"
-    open-pull-requests-limit: 4
+      interval: "monthly"
+    open-pull-requests-limit: 2
     groups:
       actions-minor-patch:
         applies-to: version-updates