fix: align fingerprint headers to match Antigravity Manager behavior

Reduce fingerprint surface to minimize rate limiting by matching what
Antigravity Manager actually sends on content requests.

Changes:
- Remove X-Goog-QuotaUser and X-Client-Device-Id headers (AM doesn't send them)
- Remove X-Goog-Api-Client and Client-Metadata from fingerprint headers (AM only sends User-Agent on content requests)
- Fix ideType: replace random pool (INTELLIJ, ANDROID_STUDIO, etc.) with ANTIGRAVITY/IDE_UNSPECIFIED
- Remove wrong SDK clients (intellij/2024.1, android-studio/2024.1, jetbrains/2024.3) from randomization pools
- Strip extra Client-Metadata fields (osVersion, arch, sqmId) not present in AM
- Force-regenerate saved fingerprints on account load to clear stale data
- Set CODE_ASSIST_METADATA.ideType to ANTIGRAVITY (matching AM)