feat(auth): install all authentication providers by default

All authentication methods (Basic Auth, Flask-Login, OAuth) are now
installed as core dependencies instead of optional extras. This
simplifies setup and eliminates the need to run `uv sync --extra auth-*`
when switching between authentication methods.

Changes:
- Move authlib, bcrypt, and flask-login to core dependencies
- Remove auth-* optional dependency groups from pyproject.toml
- Update documentation to remove installation instructions
- Simplify troubleshooting and migration guides

Benefits:
- No import errors when switching auth methods
- Simpler user experience
- All providers available out of the box

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

libtisbackup/auth/README.md

@@ -61,11 +61,6 @@ auth = get_auth_provider("basic", {
 })
 ```
 
-**Required dependencies:**
-```bash
-uv sync --extra auth-basic
-```
-
 **Features:**
 - HTTP Basic Authentication
 - bcrypt password hashing
@@ -81,11 +76,6 @@ auth = get_auth_provider("flask-login", {
 })
 ```
 
-**Required dependencies:**
-```bash
-uv sync --extra auth-login
-```
-
 **Features:**
 - Session-based authentication
 - Multiple users support
@@ -111,11 +101,6 @@ auth = get_auth_provider("oauth", {
 })
 ```
 
-**Required dependencies:**
-```bash
-uv sync --extra auth-oauth
-```
-
 **Features:**
 - OAuth2 authentication
 - Google, GitHub, GitLab support