Add GitHub profile backup feature

New feature to automatically backup K-profiles, cloud profiles, and app
settings to a GitHub repository with scheduled or on-demand execution.

Features:
- Configure GitHub repo URL and Personal Access Token
- Schedule backups hourly, daily, or weekly (background scheduler)
- Manual backup trigger with real-time progress tracking
- Skip unchanged commits (only creates commit when data changes)
- Backup history log with status and commit links
- Requires Bambu Cloud login for full profile access
- New Settings → Backup & Restore tab consolidating all backup options
- GitHub backup config included in local backup/restore (except PAT)

Backend:
- New models: GitHubBackupConfig, GitHubBackupLog
- New service: GitHubBackupService with scheduler and GitHub API client
- New routes: /github-backup/* for config, status, logs, and triggers
- Updated settings.py to include github_backup in backup/restore

Frontend:
- New GitHubBackupSettings.tsx component with auto-save
- Updated SettingsPage with Backup tab and status indicator
- Added API types and methods to client.ts

Tests:
- Backend integration tests for all GitHub backup API endpoints
- Frontend API type and endpoint tests

backend/app/schemas/github_backup.py

@@ -0,0 +1,154 @@
+"""Pydantic schemas for GitHub backup configuration."""
+
+import re
+from datetime import datetime
+from enum import Enum
+
+from pydantic import BaseModel, Field, field_validator
+
+
+class ScheduleType(str, Enum):
+    """Backup schedule types."""
+
+    HOURLY = "hourly"
+    DAILY = "daily"
+    WEEKLY = "weekly"
+
+
+class GitHubBackupConfigCreate(BaseModel):
+    """Schema for creating/updating GitHub backup config."""
+
+    repository_url: str = Field(..., min_length=1, max_length=500, description="GitHub repository URL")
+    access_token: str = Field(..., min_length=1, description="Personal Access Token")
+    branch: str = Field(default="main", max_length=100, description="Branch to push to")
+
+    schedule_enabled: bool = Field(default=False, description="Enable scheduled backups")
+    schedule_type: ScheduleType = Field(default=ScheduleType.DAILY, description="Schedule frequency")
+
+    backup_kprofiles: bool = Field(default=True, description="Backup K-profiles")
+    backup_cloud_profiles: bool = Field(default=True, description="Backup Bambu Cloud profiles")
+    backup_settings: bool = Field(default=False, description="Backup app settings")
+
+    enabled: bool = Field(default=True, description="Enable backup feature")
+
+    @field_validator("repository_url")
+    @classmethod
+    def validate_repo_url(cls, v: str) -> str:
+        """Validate GitHub repository URL format."""
+        # Accept various GitHub URL formats
+        patterns = [
+            r"^https://github\.com/[\w.-]+/[\w.-]+(?:\.git)?$",
+            r"^git@github\.com:[\w.-]+/[\w.-]+(?:\.git)?$",
+        ]
+        v = v.strip().rstrip("/")
+        if not any(re.match(p, v) for p in patterns):
+            raise ValueError("Invalid GitHub repository URL. Expected format: https://github.com/owner/repo")
+        return v
+
+
+class GitHubBackupConfigUpdate(BaseModel):
+    """Schema for updating GitHub backup config (all fields optional)."""
+
+    repository_url: str | None = Field(default=None, max_length=500)
+    access_token: str | None = Field(default=None)
+    branch: str | None = Field(default=None, max_length=100)
+
+    schedule_enabled: bool | None = None
+    schedule_type: ScheduleType | None = None
+
+    backup_kprofiles: bool | None = None
+    backup_cloud_profiles: bool | None = None
+    backup_settings: bool | None = None
+
+    enabled: bool | None = None
+
+    @field_validator("repository_url")
+    @classmethod
+    def validate_repo_url(cls, v: str | None) -> str | None:
+        if v is None:
+            return v
+        patterns = [
+            r"^https://github\.com/[\w.-]+/[\w.-]+(?:\.git)?$",
+            r"^git@github\.com:[\w.-]+/[\w.-]+(?:\.git)?$",
+        ]
+        v = v.strip().rstrip("/")
+        if not any(re.match(p, v) for p in patterns):
+            raise ValueError("Invalid GitHub repository URL")
+        return v
+
+
+class GitHubBackupConfigResponse(BaseModel):
+    """Schema for GitHub backup config API response."""
+
+    id: int
+    repository_url: str
+    has_token: bool = Field(description="Whether an access token is configured")
+    branch: str
+
+    schedule_enabled: bool
+    schedule_type: str
+
+    backup_kprofiles: bool
+    backup_cloud_profiles: bool
+    backup_settings: bool
+
+    enabled: bool
+    last_backup_at: datetime | None
+    last_backup_status: str | None
+    last_backup_message: str | None
+    last_backup_commit_sha: str | None
+    next_scheduled_run: datetime | None
+
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class GitHubBackupLogResponse(BaseModel):
+    """Schema for backup log API response."""
+
+    id: int
+    config_id: int
+    started_at: datetime
+    completed_at: datetime | None
+    status: str
+    trigger: str
+    commit_sha: str | None
+    files_changed: int
+    error_message: str | None
+
+    class Config:
+        from_attributes = True
+
+
+class GitHubBackupStatus(BaseModel):
+    """Schema for current backup status."""
+
+    configured: bool = Field(description="Whether backup is configured")
+    enabled: bool = Field(description="Whether backup is enabled")
+    is_running: bool = Field(description="Whether a backup is currently running")
+    progress: str | None = Field(default=None, description="Current backup progress message")
+    last_backup_at: datetime | None
+    last_backup_status: str | None
+    next_scheduled_run: datetime | None
+
+
+class GitHubTestConnectionResponse(BaseModel):
+    """Schema for test connection response."""
+
+    success: bool
+    message: str
+    repo_name: str | None = None
+    permissions: dict | None = None
+
+
+class GitHubBackupTriggerResponse(BaseModel):
+    """Schema for manual backup trigger response."""
+
+    success: bool
+    message: str
+    log_id: int | None = None
+    commit_sha: str | None = None
+    files_changed: int = 0