feat(search): full-history + content commit search

[danielss-dev]

What

Closes the last ◐ on the 1.0 commit-search line: full-history and content (pickaxe) search, backed by a new git log-based engine command.

The in-graph search highlighted matches over the loaded log client-side — instant, but blind past the loaded window and unable to search file contents (it holds no diffs). This adds the backend reach to close both gaps.

Backend

• Repo::search_log(query, mode, limit) (crates/strand-core/src/log.rs) shells out to git log across all refs (mirrors log's ref set + empty-repo handling; shares commit_format + the parser):
  • Message → --grep, Author → --author — both --fixed-strings -i (case-insensitive substring), reaching beyond the loaded window.
  • Content → -G (the pickaxe) — commits whose diff added/removed a matching line (the one search the client can't do).
• SearchMode enum, lowercase-serialized for IPC. +5 unit tests.

Wiring & UI

• repo_search_log IPC → repoSearchLog wrapper → searchLog store action (results in commitSearchResults).
• Commits.tsx: a Content field mode + a "Search all history" button (⌘↵, or ↵ in Content) open a keyboard-navigable results dropdown (combobox + listbox / aria-activedescendant). Clicking a hit scrolls+focuses it when loaded, and opens the detail panel either way — CommitDetail falls back to the stored results so an out-of-window commit still renders.
• The loaded-window highlight + ‹/› stay untouched; the deep search is explicit so git log -G never fires per-keystroke. Adds a "Search file contents…" palette action.

Design notes

• Flat dropdown, not graph filtering — dropping rows would break the lane topo invariant.
• One deliberate cut: -S occurrence-count pickaxe isn't exposed; -G covers the intent. Noted as a future refinement.

Verification

cargo test -p strand-core (90 pass, +5), clippy -D warnings clean, tsc clean, vitest (131), vite build ✓.

⚠️ Not verified: a live pass in the actual Tauri window (the webview can't be driven by the browser harness here).

🤖 Generated with Claude Code