fix(camera): restrict proxy to admins and add stream timeouts

[Micsi]

Motivation

• Close an authenticated SSRF/abuse vector exposed by the camera proxy by limiting who can invoke it.
• Reduce availability/exhaustion risk from unbounded upstream streams by enforcing finite HTTP client timeouts.

Description

• Add a database dependency (Database, get_db) and perform an is_admin lookup inside the camera-specific auth dependency to require admin privileges for /api/v1/camera/proxy.
• Preserve existing JWT entry points (Authorization: Bearer … header and ?_token=… query) for camera widgets while decoding the token and enforcing the admin check.
• Replace the unbounded streaming client timeout (timeout=None) with a finite httpx.Timeout(connect=5.0, read=30.0, write=10.0, pool=30.0) for the GET stream.
• Keep the existing URL scheme check, DNS-based IP denylist (_check_ssrf), and follow_redirects=False behavior to prevent redirect-based SSRF.

Testing

• Ran python -m compileall obs/api/v1/camera.py, which completed successfully and indicates the module has no syntax errors.

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Codex Task