feat(permissions): implement permission system with plan mode enforcement (M1 complete)

This commit implements the complete M1 milestone (Config & Permissions) including:

- New permissions crate with Tool, Action, Mode, and PermissionManager
- Three permission modes: Plan (read-only default), AcceptEdits, Code
- Pattern matching for permission rules (exact match and prefix with *)
- Integration with config-agent for mode-based permission management
- CLI integration with --mode flag to override configured mode
- Permission checks for Read, Glob, and Grep operations
- Comprehensive test suite (10 tests in permissions, 4 in config, 4 in CLI)

Also fixes:
- Fixed failing test in tools-fs (glob pattern issue)
- Improved glob_list() root extraction to handle patterns like "/*.txt"

All 21 workspace tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

crates/platform/permissions/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "permissions"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+serde = { version = "1", features = ["derive"] }
+thiserror = "1"