fix: discover Claude profile roots

[graykode]

Summary

• Add claude_config_dirs support for explicit Claude Code profile roots.
• Auto-discover ~/.claude and ~/.claude-* roots that contain both sessions/ and projects/.
• Wire configured roots through the app/collector stack and document the config option.

Fixes #123

Test Plan

• cargo test
• cargo clippy -- -D warnings
• cargo build

[graykode]

lgtm — security is clean (no new network/shell/deps, only adds read-only home-dir scanning). Discovery flow reuses the existing BTreeSet dedup + ConfigDir wrapping cleanly, and the #[cfg(test)] gating on the now-test-only constructors avoids dead-code noise. Build/clippy/143 tests all green, including the four new ones.

one minor inconsistency, not blocking: configured claude_config_dirs entries are dropped unless they pass is_claude_config_root (need both sessions/ and projects/), while env-based CLAUDE_CONFIG_DIR only checks is_dir(). A typo'd configured path is silently ignored with no warning — fine as a deliberate choice, just worth a note in the docs if users hit it.