feat: add Cursor, Codex, and OpenCode harnesses — maximize every AI coding tool

- AGENTS.md: universal cross-tool file read by Claude Code, Cursor, Codex, and OpenCode
- .cursor/: 15 hook events via hooks.json, 16 hook scripts with DRY adapter pattern,
  29 rules (9 common + 20 language-specific) with Cursor YAML frontmatter
- .codex/: reference config.toml, Codex-specific AGENTS.md supplement,
  10 skills ported to .agents/skills/ with openai.yaml metadata
- .opencode/: 3 new tools (format-code, lint-check, git-summary), 3 new hooks
  (shell.env, experimental.session.compacting, permission.ask), expanded instructions,
  version bumped to 1.6.0
- README: fixed Cursor section, added Codex section, added cross-tool parity table
- install.sh: now copies hooks.json + hooks/ for --target cursor

.cursor/rules/common-patterns.md

@@ -0,0 +1,35 @@
+---
+description: "Common patterns: repository, API response, skeleton projects"
+alwaysApply: true
+---
+# Common Patterns
+
+## Skeleton Projects
+
+When implementing new functionality:
+1. Search for battle-tested skeleton projects
+2. Use parallel agents to evaluate options:
+   - Security assessment
+   - Extensibility analysis
+   - Relevance scoring
+   - Implementation planning
+3. Clone best match as foundation
+4. Iterate within proven structure
+
+## Design Patterns
+
+### Repository Pattern
+
+Encapsulate data access behind a consistent interface:
+- Define standard operations: findAll, findById, create, update, delete
+- Concrete implementations handle storage details (database, API, file, etc.)
+- Business logic depends on the abstract interface, not the storage mechanism
+- Enables easy swapping of data sources and simplifies testing with mocks
+
+### API Response Format
+
+Use a consistent envelope for all API responses:
+- Include a success/status indicator
+- Include the data payload (nullable on error)
+- Include an error message field (nullable on success)
+- Include metadata for paginated responses (total, page, limit)