test(acp): snapshot scenarios for the filesystem tools

Five recorded ACP snapshot scenarios exercising read/write/edit end-to-end
through the real acp-agent subprocess, replayed keyless in CI:

- fs-read — read a seeded file (read tool + presentation + observed-state)
- fs-write — create a file (write, no prior version guard)
- fs-edit — read then literal-replace (read-before-edit authorization)
- fs-write-overwrite — read then rewrite (replaceIfVersion after a read)
- fs-read-window — read lines 5-8 with offset/limit (windowing + the offset
  surfaced as the tool_call location line)

The goldens confirm the tools render with their new presentation — Read/Write/
Edit <path> titles, read/edit kinds, and `locations` (fs-read-window carries
`{path, line:5}`) — and that the prompts steered the model to the fs tools, not
bash (zero bash calls in any golden). Recorded against the real API, filtered to
the new scenarios so no existing fixture churned.

examples/acp-agent/tests/snapshots/fs-write-overwrite/workspace/data.txt

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