feat(ci): add Criterion performance benchmarks for hot paths (#638)

Add benchmarks using Criterion for:
- XML tool-call parsing (single and multi-call)
- Native tool-call parsing
- SQLite memory store/recall/count operations
- Full agent turn cycle (text-only and with tool call)

Add CI workflow (.github/workflows/benchmarks.yml) that:
- Runs benchmarks on push to main and on PRs
- Uploads Criterion results as artifacts
- Posts benchmark summary as PR comment for regression visibility

Ref: https://github.com/zeroclaw-labs/zeroclaw/issues/618 (item 7)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/benchmarks.yml

@@ -0,0 +1,103 @@
+name: Performance Benchmarks
+
+on:
+    push:
+        branches: [main]
+    pull_request:
+        branches: [main]
+    workflow_dispatch:
+
+concurrency:
+    group: bench-${{ github.event.pull_request.number || github.sha }}
+    cancel-in-progress: true
+
+permissions:
+    contents: read
+    pull-requests: write
+
+env:
+    CARGO_TERM_COLOR: always
+
+jobs:
+    benchmarks:
+        name: Criterion Benchmarks
+        runs-on: blacksmith-2vcpu-ubuntu-2404
+        timeout-minutes: 30
+        steps:
+            - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+            - uses: dtolnay/rust-toolchain@631a55b12751854ce901bb631d5902ceb48146f7 # stable
+              with:
+                  toolchain: 1.92.0
+            - uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2
+
+            - name: Run benchmarks
+              run: cargo bench --locked 2>&1 | tee benchmark_output.txt
+
+            - name: Upload benchmark results
+              if: always()
+              uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+              with:
+                  name: benchmark-results
+                  path: |
+                      target/criterion/
+                      benchmark_output.txt
+                  retention-days: 30
+
+            - name: Post benchmark summary on PR
+              if: github.event_name == 'pull_request'
+              uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
+              with:
+                  script: |
+                      const fs = require('fs');
+                      const output = fs.readFileSync('benchmark_output.txt', 'utf8');
+
+                      // Extract Criterion result lines
+                      const lines = output.split('\n').filter(l =>
+                        l.includes('time:') || l.includes('change:') || l.includes('Performance')
+                      );
+
+                      if (lines.length === 0) {
+                        core.info('No benchmark results to post.');
+                        return;
+                      }
+
+                      const body = [
+                        '## 📊 Benchmark Results',
+                        '',
+                        '```',
+                        lines.join('\n'),
+                        '```',
+                        '',
+                        '<details><summary>Full output</summary>',
+                        '',
+                        '```',
+                        output.substring(0, 60000),
+                        '```',
+                        '</details>',
+                      ].join('\n');
+
+                      // Find and update or create comment
+                      const { data: comments } = await github.rest.issues.listComments({
+                        owner: context.repo.owner,
+                        repo: context.repo.repo,
+                        issue_number: context.payload.pull_request.number,
+                      });
+
+                      const marker = '## 📊 Benchmark Results';
+                      const existing = comments.find(c => c.body && c.body.startsWith(marker));
+
+                      if (existing) {
+                        await github.rest.issues.updateComment({
+                          owner: context.repo.owner,
+                          repo: context.repo.repo,
+                          comment_id: existing.id,
+                          body,
+                        });
+                      } else {
+                        await github.rest.issues.createComment({
+                          owner: context.repo.owner,
+                          repo: context.repo.repo,
+                          issue_number: context.payload.pull_request.number,
+                          body,
+                        });
+                      }