feat: add Cursor IDE support with pre-translated configs

Add complete .cursor/ directory with rules, agents, skills, commands,
and MCP config adapted for Cursor's format. This makes ecc-universal
a truly cross-IDE package supporting Claude Code, Cursor, and OpenCode.

- 27 rule files with YAML frontmatter (description, globs, alwaysApply)
- 13 agent files with full model IDs and readonly flags
- 30 skill directories (identical Agent Skills standard, no translation)
- 31 command files (5 multi-* stubbed for missing codeagent-wrapper)
- MCP config with Cursor env interpolation syntax
- README.md and MIGRATION.md documentation
- install.sh --target cursor flag for project-scoped installation
- package.json updated with .cursor/ in files and cursor keywords

.cursor/commands/checkpoint.md

@@ -0,0 +1,74 @@
+# Checkpoint Command
+
+Create or verify a checkpoint in your workflow.
+
+## Usage
+
+`/checkpoint [create|verify|list] [name]`
+
+## Create Checkpoint
+
+When creating a checkpoint:
+
+1. Run `/verify quick` to ensure current state is clean
+2. Create a git stash or commit with checkpoint name
+3. Log checkpoint to `.cursor/checkpoints.log`:
+
+```bash
+echo "$(date +%Y-%m-%d-%H:%M) | $CHECKPOINT_NAME | $(git rev-parse --short HEAD)" >> .cursor/checkpoints.log
+```
+
+4. Report checkpoint created
+
+## Verify Checkpoint
+
+When verifying against a checkpoint:
+
+1. Read checkpoint from log
+2. Compare current state to checkpoint:
+   - Files added since checkpoint
+   - Files modified since checkpoint
+   - Test pass rate now vs then
+   - Coverage now vs then
+
+3. Report:
+```
+CHECKPOINT COMPARISON: $NAME
+============================
+Files changed: X
+Tests: +Y passed / -Z failed
+Coverage: +X% / -Y%
+Build: [PASS/FAIL]
+```
+
+## List Checkpoints
+
+Show all checkpoints with:
+- Name
+- Timestamp
+- Git SHA
+- Status (current, behind, ahead)
+
+## Workflow
+
+Typical checkpoint flow:
+
+```
+[Start] --> /checkpoint create "feature-start"
+   |
+[Implement] --> /checkpoint create "core-done"
+   |
+[Test] --> /checkpoint verify "core-done"
+   |
+[Refactor] --> /checkpoint create "refactor-done"
+   |
+[PR] --> /checkpoint verify "feature-start"
+```
+
+## Arguments
+
+$ARGUMENTS:
+- `create <name>` - Create named checkpoint
+- `verify <name>` - Verify against named checkpoint
+- `list` - Show all checkpoints
+- `clear` - Remove old checkpoints (keeps last 5)