feat: implement session capture adapters

[aroff]

Summary

• Add the aikit-session-capture workspace crate for Claude Code, Codex, and OpenCode passive transcript capture.
• Wire passive capture capabilities, capture API routes, SQLite storage, MCP tools, and watcher support.
• Add client-side cost extraction and update stale session-capture spec implementation status.

Validation

• cargo test --workspace --features mcp-tools,crossmount
• cargo clippy -p aikit-session-capture --features default,crossmount,mcp-tools,watcher --all-targets -- -D warnings
• cargo check -p aikit-cli --features default,mcp-tools,crossmount
• pre-commit hook passed
• pre-push hook passed