chore: remove unused legacy Dockerfiles (#2314)

Fixes #2310. Partial follow-up to #1385 (PR-C).

Remove unused `Dockerfile.go` and `Dockerfile.node`, which describe
retired alternate builds. Current workflows, Makefile, Compose variants
and operator scripts already select the canonical `Dockerfile`.

Remove the obsolete formatter exclusions and label the old Node-to-Go
migration guide historical, linking current deployment instructions.
Historical release prose remains untouched. The canonical image, runtime
files, dependencies and Compose behavior are unchanged.

Validation: audited all 1,501 tracked files; old and new formatter
inputs are exactly the same 633 real Go files. Both formatter commands,
YAML/shell/workflow-reference checks, existing workflow/routing tests,
COPY gate and test inventory pass. All 218 standalone frontend suites
pass. The unchanged backend tree passed full server/ingestor suites, and
the unchanged app passed 12 browser smoke cases.

TDD exemption: behavior-preserving cleanup/refactor plus documentation;
no test files modified. `make` and `actionlint` were unavailable
locally; equivalent formatter and focused workflow checks ran directly.

[CI passed on this
head](https://github.com/Kpa-clawbot/CoreScope/actions/runs/40230911566),
including canonical container builds and all browser shards. Three
independent reviews passed. The published historical guide and its
current-deployment links render correctly in Chromium. No
settings/customizer changes.

.github/workflows/deploy.yml

@@ -172,9 +172,8 @@ jobs:
       - name: Enforce gofmt + go vet (issue #1859)
         run: |
           set -e
-          # gofmt: every tracked *.go file except the misnamed Dockerfile.go,
-          # which is a Dockerfile (FROM ...) that gofmt cannot parse.
-          unformatted=$(gofmt -l $(git ls-files '*.go' | grep -vi 'Dockerfile.go'))
+          # gofmt: every tracked *.go file.
+          unformatted=$(gofmt -l $(git ls-files '*.go'))
           if [ -n "$unformatted" ]; then
             echo "::error::gofmt required on these files:"
             echo "$unformatted"