Run the performance workflow only on demand

Dependency bumps triggered the whole gate suite on every pull request,
which cost runner time and surfaced unrelated NFR-1-external failures.
Drop the push, pull_request and schedule triggers so the workflow starts
only from workflow_dispatch, and remove the now-unreachable
pull_request guards on the native jobs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: IRus

.github/workflows/performance.yml

@@ -1,12 +1,6 @@
 name: Performance
 
 on:
-  push:
-    branches:
-      - main
-  pull_request:
-  schedule:
-    - cron: "17 4 * * 1"
   workflow_dispatch:
 
 permissions:
@@ -101,7 +95,6 @@ jobs:
 
   native:
     name: ${{ matrix.target }} performance gates
-    if: github.event_name != 'pull_request'
     runs-on: ${{ matrix.runner }}
     timeout-minutes: 120
     strategy:
@@ -161,7 +154,6 @@ jobs:
 
   compiled-reference:
     name: ${{ matrix.target }} Wasmtime compiled reference
-    if: github.event_name != 'pull_request'
     runs-on: ${{ matrix.runner }}
     timeout-minutes: 120
     strategy: