spec 013-acp: several current-state sections still assert outdated agent-client-protocol version

[bug-ops]

Description

`specs/013-acp/spec.md` was found during the PR #6629 specs audit to have roughly 15 body locations that still assert `agent-client-protocol 1.0.1` / `schema =1.1.0` as the current state, even though a later changelog entry in the same file records the bump to `1.2.0` / `schema =1.4.0`. This wasn't a single find/replace fix because the file mixes historical-narrative sections (correctly `1.0.1`, describing what shipped at the time) with current-state sections (which should read `1.2.0`), and a careless global replace would corrupt the historical narrative.

Reproduction Steps

1. `grep -n "1.0.1\|=1.1.0" specs/013-acp/spec.md`
2. Cross-check each hit against `Cargo.toml`'s pinned `agent-client-protocol` version and the file's own changelog entry recording the `1.2.0` bump
3. Observe several current-state sections still read the old version

Expected Behavior

Current-state sections consistently reflect the actual pinned `agent-client-protocol` version; historical-narrative sections remain unchanged as an accurate record of what shipped at each point in time.

Actual Behavior

Mixed — some sections correctly updated, most still reference the superseded version.

Environment

• Version: main branch, spec audit as of PR docs(specs): correct stale references, broken links, and formatting #6629
• Features: acp

Logs / Evidence

See PR #6629 description, "Flagged, not executed" section, item 3.