Fix Anthropic rejection of built-in tool input schemas

[lukebuehler]

Anthropic rejects requests advertising blob_put, Write, or VfsWrite because their input schemas contain top-level oneOf constraints, including in sessions with code mode disabled. Remove those constraints from the shared blob and file-writer schemas while preserving the descriptions and runtime validation that require exactly one input. Binary/reference writes, provider-specific arguments, and blob-tool availability are preserved.

Adds three live regressions and checks assembled Anthropic toolsets with code mode enabled and disabled. Extends invalid blob-input coverage and regenerates the captured provider requests; fixture changes only remove the affected top-level constraints.

Validation:

• cargo test -p tools --locked --quiet
• cargo test -p llm-runtime --locked --quiet (credentialed suites remain ignored)
• All three live schema regressions and the baseline generation test pass with ANTHROPIC_MESSAGES_MODEL=claude-opus-5-5.
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo fmt --all -- --check
• git diff --check