dev-inf: Enable AI review for all PRs except backports

Changed the workflow trigger condition from opt-in (O-AI-Review label)
to opt-out, with automatic exclusions for:
- Backport PRs (detected by checking if base ref starts with 'release-')
- PRs with O-No-AI-Review label (manual opt-out)

This enables broader AI review coverage while avoiding redundant
reviews of backported changes and respecting explicit opt-outs.

The base ref check avoids a race condition where Blathers adds the
backport label after the PR is opened.

Release note: none

Epic: None

Author: ajstorm

.github/workflows/pr-analyzer-threestage.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   claude-code-pr-review:
     runs-on: ubuntu-latest
-    if: contains(github.event.pull_request.labels.*.name, 'O-AI-Review')
+    if: "!startsWith(github.base_ref, 'release-') && !contains(github.event.pull_request.labels.*.name, 'O-No-AI-Review')"
     permissions:
       contents: read
       pull-requests: write