docs: port #13339 to V2 — Antigravity attachments reach the agent by path

Main's #13339 changed V1's Antigravity adapter to pass unsupported files by
path, and the merge brought its doc text, which describes V1's native
PDF, text, and audio limits. V2's Antigravity runs through AcpAdapterV2,
which embeds only images and passes every other attachment as a saved
path (AttachmentPrompt.providerMessageTextWithAttachmentPaths), with reads
confined by AntigravityClientFiles. The V1 support code merged but has no
V2 caller. The provider page now describes V2's behavior.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: juliusmarminge

docs/user/providers-antigravity.md

@@ -92,14 +92,9 @@ Skills for every project go in `~/.gemini/config/skills` or
 `~/.gemini/antigravity-cli/skills`. Antigravity does not read `~/.agents/skills`,
 so a skill there only appears when the project itself is your home directory.
 
-Antigravity accepts images, PDFs, text files, and supported audio formats directly.
-Its limits are 1 MiB per text file, 10 MiB per image, 20 MiB per audio clip, and
-50 MiB total native attachments per message. PDFs, text, and audio that exceed
-their native limits or the remaining native budget are passed as file paths
-for the agent to inspect with tools. ZIP archives and videos also use file paths.
-These files do not count toward the native attachment budget or enable native video input.
-Unsupported image formats are rejected. The native limits can be lower than
-the general upload limit.
+Antigravity receives images directly. Every other attachment, including PDFs,
+text, audio, archives, and videos, is passed as a saved file path for the agent
+to inspect with its tools. A video path does not enable native video input.
 
 ### Subagents