Test 1183 — release version-sync dry-run completion

Source commit under test:
ee31dfdf8afb9e309052b4ecfa0b923704c0ca22

Scope:
- scripts/sync-pinned-versions.sh treats diff rc=1 as an expected preview.
- Every registered target is processed and the dry-run summary is printed.
- A genuine diff rc>1 remains fatal and reports the failing target/status.
- The preview is limited without a sed/head SIGPIPE under pipefail.
- The two release-pair package mappings point at writable quoted literals:
  `PAIRED_AGENT_NETWORK_VERSION` and `PAIRED_AGENT_NODE_VERSION`.
- Stale documentation registrations with no remaining literal pin are removed.
- A compatibility alias such as `const OLD = NEW` is rejected as missing,
  rather than being mistaken for a writable version target.

Docker command:
sg docker -c 'docker build --build-arg SOURCE_COMMIT=ee31dfdf8afb9e309052b4ecfa0b923704c0ca22 -t anet-test1183-rev2-ee31dfdf -f tests/test1183-sync-pinned-dryrun/Dockerfile . && docker run --rm --network none anet-test1183-rev2-ee31dfdf'

Result:
PASS: normal version differences do not abort the dry-run
PASS: every registered target is followed by the final summary
PASS: both release-pair registries own writable quoted literals
PASS: a constant name without a quoted literal is rejected as stale
PASS: WITNESSED_RED: the old diff pipeline exits early and loses the summary
PASS: real diff failures remain nonzero and visible
SOURCE_COMMIT=ee31dfdf8afb9e309052b4ecfa0b923704c0ca22
RESULT: PASS

Witnessed-red construction:
The test makes a disposable copy of the source script and replaces the new
explicit diff-status block with the previous one-line pipeline:

  diff -u ... | sed ... | head -40

The mutation target must be found exactly; the mutated script then exits
nonzero on the real preview.44 -> preview.45 difference and never emits the
dry-run summary. The committed source exits zero and emits that summary.

Real-error negative control:
PATH is prefixed with a disposable diff executable that exits 2. The source
script stays nonzero and prints `ERROR: diff failed ... (rc=2)`, proving that
the fix does not turn all diff failures green.

Registry-drift negative control:
The baseline must contain `WOULD-WRITE` for the real paired network literal;
merely enumerating a filename is insufficient. A disposable script then
changes the registry back to the non-literal compatibility alias
`OPENCODE_AGENT_NETWORK_VERSION`. The run exits nonzero and names that exact
alias as `MISSING TARGET`, proving a constant name alone cannot satisfy the
registry. The agent-node package is independently dry-run to preview.34 and
must also produce `WOULD-WRITE` plus the final summary.

Boundaries:
- No package version was changed.
- No npm package or dist-tag was published.
- PR #1178 files were not modified.
- No production or global npm installation was touched.
