feat(fs): add a minimal read_image tool over the attachment and fs seams

The model reads a PNG/JPEG/WebP/GIF file, the bytes commit through the
durable attachment lifecycle, and the tool result carries the real
ImageBlock so the image enters context from the next request onward.
FileSystem gains a bounded readBytes primitive (local + E2B providers);
registration is conditional on the attachment store, and a strict
execution gate refuses routes that do not declare image input, so a
text route's durable history stays free of image blocks. llm-replay
models may declare inputModalities, letting keyless ACP snapshots pin
both the sha256-referenced success and the verbatim refusal.

Supersedes the withdrawn route-scoped design of PR #598; the decision
record is .agents/notes/implemented/feature/2026-08-10-minimal-read-image-tool.md.

scripts/gen-cordis-catalog.ts

@@ -460,6 +460,7 @@ export const FOUNDATION_TYPE_NAMES: ReadonlySet<string> = new Set([
   'Promise',
   'Record',
   'Readonly',
+  'Uint8Array',
 ])
 
 /** Project types deliberately documented outside the subsystems catalog. */