feat: add opencode agents and skills for development workflows

New agents:
- architect: system design, module interactions, data flow
- debugger: crash/memory/thread debugging with ASan, TSan, valgrind, gdb
- security-auditor: TLS, input validation, buffer safety, crypto audit
- refactorer: DRY, separation of concerns, API simplification
- integrator: integration tests, CI/CD pipeline, end-to-end verification
- code-explainer: architecture walkthrough, code explanation

New skills:
- debug-workflow: structured debugging workflow
- refactor: code restructuring with test verification
- security-audit: full security review with checklist
- benchmark: performance benchmarking with multi-run medians
- release: version bump, tests, tagging

Improved existing:
- c-reviewer: added security checklist
- cmake-expert: added ASan/TSan/UBSan configs, ccache, cross-compilation
- perf-analyst: added perf/valgrind/gprof commands
- test-writer: added fuzzing harnesses, integration test patterns
- pr-build: added sanitizer build variants
- pr-review: added security review, performance impact assessment

.opencode/skills/release/SKILL.md

@@ -0,0 +1,110 @@
+---
+name: release
+description: Prepares a FastSync release — version bump, changelog, build verification, and git tagging. Use when the user says "prepare release", "bump version", "tag release", or wants to cut a new version.
+---
+
+# Release Skill
+
+Prepares a new release of FastSync. This skill CAN edit files, commit, and tag.
+
+## Workflow
+
+### Step 1: Determine Version
+
+Ask the user or determine from context:
+- **Major** (X.0.0) — breaking protocol changes, incompatible CLI changes
+- **Minor** (x.Y.0) — new features, backward compatible
+- **Patch** (x.y.Z) — bug fixes, no protocol changes
+
+Current version: `PROTOCOL_VERSION "1.1.0"` in `src/shared/config.h`
+
+### Step 2: Check Protocol Version
+
+If the wire protocol changed, bump `PROTOCOL_VERSION` in `src/shared/config.h`:
+```c
+#define PROTOCOL_VERSION "1.2.0"  // or "2.0.0" for breaking
+```
+
+Protocol version changes require:
+- Both client and server to be updated together
+- Backward compatibility considerations documented
+- Migration path clear
+
+### Step 3: Verify Build and Tests
+
+```bash
+rm -rf build
+cmake -B build -S .
+cmake --build build -j$(nproc)
+./build/tests
+python3 test.py
+```
+
+ALL tests must pass before release.
+
+### Step 4: Run Sanitizer Checks
+
+```bash
+# ASan
+rm -rf build
+cmake -B build -S . \
+  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
+  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
+cmake --build build -j$(nproc)
+./build/tests
+```
+
+### Step 5: Update README (If Needed)
+
+Check if README needs updates:
+- New features documented
+- New CLI flags documented
+- Benchmark results updated
+- Build instructions current
+
+### Step 6: Create Release Commit
+
+```bash
+git add -A
+git commit -m "Release vX.Y.Z
+
+- <list of changes>
+- Protocol version: X.Y.Z
+- Tested: unit tests, integration tests, ASan"
+```
+
+### Step 7: Tag the Release
+
+```bash
+git tag -a vX.Y.Z -m "Release vX.Y.Z"
+```
+
+### Step 8: Push
+
+```bash
+git push origin main --tags
+```
+
+### Step 9: Report
+
+```
+=== RELEASE SUMMARY ===
+Version: vX.Y.Z
+Protocol: X.Y.Z
+Commit: <hash>
+Tag: vX.Y.Z
+Changes:
+  - <list of changes in this release>
+Build: PASS
+Tests: PASS (<passed>/<total>)
+ASan: CLEAN
+```
+
+## Rules
+- DO verify all tests pass before release
+- DO run sanitizer checks before release
+- DO update README if features changed
+- DO tag releases with annotated tags
+- DON'T release if tests fail
+- DON'T skip sanitizer checks
+- DON'T change code during release (only version bump + docs)