feat(git-diff): rebuild Source Control window for VSCode parity + AI integration roadmap

[erdembas]

Closes #37.

Summary

This PR delivers a fullscreen, VSCode-parity Source Control window for RunHQ and plans the next chapter (OpenAI-compatible AI assistant) on top of it. Two commits, two concerns, one goal: make day-to-day Git work in RunHQ feel like a real dev tool, and lay the runway for AI surfaces that fit into the flow instead of bolting a chat box on the side.

The initial diff viewer landed as 8ae019a feat(git-diff): add git diff viewer …. Everything else here is the polish, structure, and roadmap that turns it from "works" into "lives there".

What changed

feat(git-diff): rebuild Source Control window for VSCode parity (f42b045)

• Tabs reshuffled — Commit (now also owns the file browser the old Changes tab had — they were 90% the same data), Branches (promoted out of being a sub-mode), History, Graph. Less duplication, clearer purpose per tab.
• Commit panel got file search, tree/list toggle, expand/collapse all, status legend, hover-to-stage, and a right-click context menu per file: Open / Reveal / Copy Path / Copy Relative / Stage / Unstage / Discard. Discard is gated behind ConfirmDialog; untracked deletes require typing delete before the button enables — destructive ops are never one mis-click away.
• New discard_file core op auto-routes tracked paths through git checkout HEAD -- (after a defensive git reset HEAD -- to drop staged hunks first) and untracked paths through git clean -f -d --. Exposed as git_discard_file IPC + ipc.gitDiscardFile. 53 Rust unit tests still green.
• BranchPicker (new shadcn-style component) replaces every native <select> across GraphPanel, HistoryPanel, and BranchesPanel. Portal-rendered, auto-flipping, type-ahead search, keyboard nav (↑/↓/↵/Esc), grouping. One component, four tabs, consistent UX.
• Graph commit search — type a substring (subject / author / email / hash / refs) and non-matching commits dim to ~30% opacity instead of being filtered out. Lane topology never reshuffles, so spatial memory holds. Live matched / total counter in the header.
• Layered Esc in DiffViewer — first defers to any open overlay (role="alertdialog" | "menu" | "dialog" | "listbox"), so reflexive Esc dismisses popovers / context menus / branch pickers first. Only when nothing nested is open does it pop a close-confirm before tearing the window down. Saves users from nuking a half-typed commit message because they reflex-pressed Esc to close a tooltip. The titlebar X still closes immediately — a deliberate click is a deliberate close.
• Full-file diff context (-U100000) so reviewers see the whole file, not just hunks. Toggleable via store.
• Status serialization fix — Rust FileDiffStatus was serializing as CamelCase but the frontend expected lowercase, so the M/A/D/R/C/U letters silently never rendered. Added #[serde(rename_all = \"lowercase\")]. Status letters and icons now actually show up.
• Color consistency — every panel surface unified to bg-surface-raised, inputs to bg-surface. No more opacity-stacked muted layers fighting each other across tabs.
• Material Icon Theme integration via @iconify/react + @iconify-json/material-icon-theme for file-type icons. Resizable sidebars (320–600px) with localStorage persistence.

docs(roadmap): plan OpenAI-compatible AI integration (Phase 6–8) (4a43935)

A new section in ROADMAP.md for a BYOK, OpenAI-API-compatible AI layer — provider-agnostic by design (OpenAI, Azure, OpenRouter, Together, Groq, DeepSeek, Mistral, Ollama, LM Studio, llama.cpp), so users keep their own keys and we never become a billing relay or a data hop.

Headline pieces:

• Foundations — Provider Profiles with per-feature model routing, OS-keychain credential storage, streaming-first via Tauri channels with cancellation, token/cost telemetry with monthly soft/hard limits, privacy switches (per-project AI off, local-only network mode, pre-flight secret redaction with a "preview before send" panel), offline-tolerant degradation.
• AI Surfaces (in dependency order) — Commit Message Generator (Phase 6 quick-win, rides on the Source Control window in this very PR) → Branch Name Suggester → Diff Explainer → Log Triage → PR Description / Release Notes → Code Review on Diff (suggestions only) → Project Q&A chat with auto-injected context + slash commands (/explain, /test, /diff, /run — never auto-execute) → Cross-Project Q&A backed by the existing dashboard data → Smart Auto-Tagging → Health-Check Policy Advisor.
• Operational Surfaces — editable prompt library (no black-box prompts), local SQLite per-project conversation history, "Preview Before Send" disclosure, function calling/tools later behind explicit consent.
• Technical Notes — headless runhq-core::ai module (Provider trait + OpenAICompatible impl), typed AIEvent stream (Delta / Tool / Done { usage }), static model registry for context windows + per-1k pricing, failure budget (30s timeout, 2-retry exponential backoff, per-profile circuit breaker), no background calls without explicit user action.

Implementation order updated:

Phase	Features
Phase 6	AI Foundations + Commit Messages
Phase 7	AI Diff & Log Triage, PR Drafting
Phase 8	AI Project & Cross-Project Q&A

Marked Git Diff Viewer as ~~shipped~~ in the existing phase table.

Why two commits

• feat is reviewable as a single Source Control deliverable — open the window, click around, all of it works without touching the roadmap.
• docs is a planning artifact reviewable on its own merits — no risk of "approve the code, oh and also approve the AI plan I didn't notice".

Test plan

• Open a project with a dirty working tree → click the Source Control toggle → window opens fullscreen.
• Commit tab: tree + list toggles work; file search filters live; expand/collapse all behave; status legend renders M/A/D/R/C/U with colors.
• Right-click a tracked modified file → context menu shows Open / Reveal / Copy Path / Copy Relative / Stage / Unstage / Discard. Discard pops ConfirmDialog. Confirming reverts the file.
• Right-click an untracked file → Discard label reads "Delete from disk", button is disabled until you type delete. Confirming removes the file via git clean -f -d --.
• Branches tab: both base and head selectors are the new BranchPicker (portal popover, type-ahead search, keyboard nav with ↑/↓/↵/Esc, groups for local/remote).
• History tab: branch filter is BranchePicker; commit search filters live.
• Graph tab: branch filter is BranchPicker; commit search dims non-matches (graph topology unchanged); matched / total count visible.
• Esc behavior — open the diff window, open any popover/menu/branch picker → press Esc → only the overlay closes, window stays. Press Esc again with nothing open → close-confirm dialog appears. Click the titlebar X → closes immediately, no confirm.
• Diff display — full-file context renders (not just hunks); no diff --git / index preamble lines leak into Monaco.
• Theme switch — flip light/dark while the diff viewer is open; Monaco + panels follow without reload.
• Backend — cargo test -p runhq-core ⇒ 53 passing (verified locally).

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