chore: add multi-agent editor config and UBS file-write hook

Add rule/config files for Cursor, Cline, Codex, Gemini, Continue, and
OpenCode editors pointing them to project conventions, UBS usage, and
AGENTS.md. Add a Claude Code on-file-write hook that runs UBS on
supported source files after every save.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gemini/rules

@@ -0,0 +1,50 @@
+
+````markdown
+## UBS Quick Reference for AI Agents
+
+UBS stands for "Ultimate Bug Scanner": **The AI Coding Agent's Secret Weapon: Flagging Likely Bugs for Fixing Early On**
+
+**Install:** `curl -sSL https://raw.githubusercontent.com/Dicklesworthstone/ultimate_bug_scanner/master/install.sh | bash`
+
+**Golden Rule:** `ubs <changed-files>` before every commit. Exit 0 = safe. Exit >0 = fix & re-run.
+
+**Commands:**
+```bash
+ubs file.ts file2.py                    # Specific files (< 1s) — USE THIS
+ubs $(git diff --name-only --cached)    # Staged files — before commit
+ubs --only=js,python src/               # Language filter (3-5x faster)
+ubs --ci --fail-on-warning .            # CI mode — before PR
+ubs --help                              # Full command reference
+ubs sessions --entries 1                # Tail the latest install session log
+ubs .                                   # Whole project (ignores things like .venv and node_modules automatically)
+```
+
+**Output Format:**
+```
+⚠️  Category (N errors)
+    file.ts:42:5 – Issue description
+    💡 Suggested fix
+Exit code: 1
+```
+Parse: `file:line:col` → location | 💡 → how to fix | Exit 0/1 → pass/fail
+
+**Fix Workflow:**
+1. Read finding → category + fix suggestion
+2. Navigate `file:line:col` → view context
+3. Verify real issue (not false positive)
+4. Fix root cause (not symptom)
+5. Re-run `ubs <file>` → exit 0
+6. Commit
+
+**Speed Critical:** Scope to changed files. `ubs src/file.ts` (< 1s) vs `ubs .` (30s). Never full scan for small edits.
+
+**Bug Severity:**
+- **Critical** (always fix): Null safety, XSS/injection, async/await, memory leaks
+- **Important** (production): Type narrowing, division-by-zero, resource leaks
+- **Contextual** (judgment): TODO/FIXME, console logs
+
+**Anti-Patterns:**
+- ❌ Ignore findings → ✅ Investigate each
+- ❌ Full scan per edit → ✅ Scope to file
+- ❌ Fix symptom (`if (x) { x.y }`) → ✅ Root cause (`x?.y`)
+````