Feature request: env var(s) to configure storage directory(ies) #473

Currently context-mode stores data in platform-specific directories under ~/.{platform}/context-mode/ (e.g. ~/.pi/, ~/.claude/), split across two locations:

• Session events → adapter-detected platform dir
• Content index (FTS5 BM25) → always ~/.claude/context-mode/content/
• Session stats → ~/.claude/context-mode/sessions/

For users running non-native harnesses (e.g. Oh My Pi/OMP which shares the Pi adapter path), or users who want all context-mode data in a single custom directory, there is currently no way to redirect storage.

Request: Add one or more environment variables to override storage paths.

Preferred approach — single root env var:

CONTEXT_MODE_DIR=~/.omp/context-mode

This would redirect all three (session events DB, content index, session stats) under that root. Falls back to the current platform-detected path when unset.

Alternative — individual overrides:

• CONTEXT_MODE_SESSION_DIR — session events database
• CONTEXT_MODE_CONTENT_DIR — BM25 FTS5 content index
• CONTEXT_MODE_STATS_DIR — process-level stats JSON files

This would allow OMP, Pi, Claude Code, and other harnesses to coexist without sharing or conflicting over storage directories.

Happy to submit a PR if this direction is agreeable.