fix(scripts): make --result_dir absolute in server-conformance.sh

[PerryLink]

scripts/server-conformance.sh resolves --result_dir only once, so a relative path — exactly the form CONTRIBUTING.md:64 documents — writes every result into a nested copy of itself.

"$CONTRIBUTING.md:64"  ->  scripts/server-conformance.sh --result_dir ./conformance-results

:63 creates the directory, :64 makes it WORKDIR, and then :95/:101 run the tests from inside that directory while passing --output-dir "$RESULT_DIR" (:99/:105). A relative $RESULT_DIR therefore resolves against itself: <dir>/<dir>/.

Measured on Windows / Git Bash:

$ bash scripts/server-conformance.sh --result_dir relout
... Total: 40 passed, 0 failed          # exit 0

$ ls relout
relout/                                  # only this
$ ls relout/relout | head -3
account-usage-configuration
...                                      # all 30 scenario dirs in here

$ bash scripts/server-conformance.sh --result_dir relout2   # with this patch
$ ls relout2 | head -3
account-usage-configuration              # 30 dirs directly, no nesting

The run still reports success, which is why nobody noticed: the results are real, just one level down from where the documented command says they are.

The change

This is the block scripts/client-conformance.sh:58-62 already has — added there by #1366 (2026-10-14) and the server script was missed:

     mkdir -p "$RESULT_DIR"
+    # Make the path absolute: the tests run from inside it (see below).
+    RESULT_DIR=$(cd "$RESULT_DIR" && pwd)
     WORKDIR="$RESULT_DIR"

Two lines in one file, taking the absolute path so the later cd "$WORKDIR" cannot change what --output-dir refers to. Cobbled from the client script verbatim, comment included, so the two stay recognisably the same fix.

Scope

• Not touched: the missing $(go env GOEXE) on the server binary at :70. I checked before ruling it out — unlike the client path, nothing spawns the server through cmd.exe, and Git Bash executes the extensionless PE, so it is not a defect.
• Duplicate check: commits?path=scripts/server-conformance.sh (3 commits, last 2026-07-14) and a search for result_dir (only scripts: fix client-conformance.sh on Windows and with a relative --result_dir #1366 and scripts: add conformance test runner #694) found no open PR, no open issue and no merged fix for the server side. The CONTRIBUTING.md:64 line that documents the relative form is unchanged since it was written.