fix(ci): finalize PR notification design (remove octo-pr-feed + fix result-notify) (#32)

## Summary

Finalizes the PR notification design. Clean, no-overlap ownership:

| Workflow | Trigger | Sends to |
|----------|---------|----------|
| `octo-pr-result-notify.yml` | `[closed]` + `pull_request_review:
[submitted]` | **global pr-feed** (`vars.OCTO_PR_FEED_GROUP_ID` with
fallback) |
| `octo-pr-review-feed.yml` | `[ready_for_review, review_requested]` |
project group (repo-specific) |

### Design decisions (per product owner)

- **`opened`/`reopened` events are not monitored** — only terminal
states (merged/closed) and review outcomes
- `octo-pr-feed.yml` is deleted — it was added in a prior pass but is
not needed under the final design

### Changes

- **`octo-pr-feed.yml`**: deleted
- **`octo-pr-result-notify.yml`**:
  - Trigger: `[closed, reopened]` → `[closed]` (terminal state only)
  - `event_kind`: simplified to `pr_merged | pr_closed`
- `feed_group_id`: `${{ vars.OCTO_PR_FEED_GROUP_ID ||
'1c303c142e9840f2a9b46c10b0972e8d' }}` (org variable with safe fallback)

No application code modified.

Co-authored-by: lml2468 <lml2468@users.noreply.github.com>

Author: lml2468

.github/workflows/octo-pr-feed.yml

@@ -2,7 +2,7 @@ name: Octo PR Result Notify
 
 on:
   pull_request_target:
-    types: [closed, reopened]
+    types: [closed]
   pull_request_review:
     types: [submitted]
 
@@ -18,11 +18,11 @@ jobs:
       pr_title: ${{ github.event.pull_request.title }}
       pr_url: ${{ github.event.pull_request.html_url }}
       pr_author: ${{ github.event.pull_request.user.login }}
-      event_kind: ${{ github.event.action == 'closed' && github.event.pull_request.merged == true && 'pr_merged' || github.event.action == 'closed' && 'pr_closed' || 'pr_reopened' }}
+      event_kind: ${{ github.event.pull_request.merged == true && 'pr_merged' || 'pr_closed' }}
       pr_additions: ${{ github.event.pull_request.additions }}
       pr_deletions: ${{ github.event.pull_request.deletions }}
       pr_changed_files: ${{ github.event.pull_request.changed_files }}
-      feed_group_id: "bdc0df15fdb346508e4281f3df55f749"
+      feed_group_id: ${{ vars.OCTO_PR_FEED_GROUP_ID || '1c303c142e9840f2a9b46c10b0972e8d' }}
     secrets:
       OCTO_BOT_TOKEN: ${{ secrets.OCTO_BOT_TOKEN }}
 
@@ -40,6 +40,6 @@ jobs:
       pr_author: ${{ github.event.pull_request.user.login }}
       event_kind: ${{ github.event.review.state == 'approved' && 'review_approved' || 'review_changes_requested' }}
       reviewer: ${{ github.event.review.user.login }}
-      feed_group_id: "bdc0df15fdb346508e4281f3df55f749"
+      feed_group_id: ${{ vars.OCTO_PR_FEED_GROUP_ID || '1c303c142e9840f2a9b46c10b0972e8d' }}
     secrets:
       OCTO_BOT_TOKEN: ${{ secrets.OCTO_BOT_TOKEN }}