feat(tools): add session management tools for OpenCode sessions (#227)

* feat(tools): add session management tools for OpenCode sessions

- Add session_list tool for listing sessions with filtering
- Add session_read tool for reading session messages and history
- Add session_search tool for full-text search across sessions
- Add session_info tool for session metadata inspection
- Add comprehensive tests for storage, utils, and tools
- Update documentation in AGENTS.md

Closes #132

* fix(session-manager): add Windows compatibility for storage paths

- Create shared/data-path.ts utility for cross-platform data directory resolution
- On Windows: uses %LOCALAPPDATA% (e.g., C:\Users\Username\AppData\Local)
- On Unix: uses $XDG_DATA_HOME or ~/.local/share (XDG Base Directory spec)
- Update session-manager/constants.ts to use getOpenCodeStorageDir()
- Update hook-message-injector/constants.ts to use same utility
- Remove dependency on xdg-basedir package in session-manager
- Follows existing pattern from auto-update-checker for consistency

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Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/features/hook-message-injector/constants.ts

@@ -1,8 +1,6 @@
 import { join } from "node:path"
-import { homedir } from "node:os"
+import { getOpenCodeStorageDir } from "../../shared/data-path"
 
-const xdgData = process.env.XDG_DATA_HOME || join(homedir(), ".local", "share")
-
-export const OPENCODE_STORAGE = join(xdgData, "opencode", "storage")
+export const OPENCODE_STORAGE = getOpenCodeStorageDir()
 export const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
 export const PART_STORAGE = join(OPENCODE_STORAGE, "part")