feat: Add Git page with branch selector, commit history, and diff viewer

Includes FileTree, CommitList, BranchSelector and DiffViewer components,
Git API routes, and mobile keyboard visibility handling for FAB buttons

frontend/src/types/git.ts

@@ -0,0 +1,70 @@
+export interface FileChange {
+  path: string
+  status: 'added' | 'modified' | 'deleted' | 'renamed' | 'copied' | 'untracked'
+  oldPath?: string
+  staged: boolean
+}
+
+export interface GitStatus {
+  branch: string
+  staged: FileChange[]
+  unstaged: FileChange[]
+  untracked: string[]
+  ahead: number
+  behind: number
+}
+
+export interface CommitInfo {
+  sha: string
+  shortSha: string
+  author: string
+  email: string
+  timestamp: number
+  message: string
+  body?: string
+  files?: FileDiff[]
+}
+
+export interface DiffLine {
+  type: 'context' | 'add' | 'delete'
+  content: string
+}
+
+export interface DiffHunk {
+  oldStart: number
+  oldLines: number
+  newStart: number
+  newLines: number
+  header?: string
+  lines: DiffLine[]
+}
+
+export interface FileDiff {
+  path: string
+  oldPath?: string
+  status: 'added' | 'modified' | 'deleted' | 'renamed'
+  isBinary: boolean
+  hunks: DiffHunk[]
+}
+
+export interface DiffResult {
+  raw: string
+  files: FileDiff[]
+}
+
+export interface BranchInfo {
+  name: string
+  isCurrent: boolean
+  isRemote: boolean
+}
+
+export interface CompareResult {
+  base: string
+  head: string
+  files: FileDiff[]
+  stats: {
+    filesChanged: number
+    additions: number
+    deletions: number
+  }
+}