fix(lint): delete dead ws broadcast cluster; demote phase-header comments

golangci-lint had been failing invisibly behind the earlier CI gate
failures. Default-build lint is now clean:

- Delete the unused pre-topic-limiter rate-limit constants, the unused
  bluemonday sanitizer, and the dead broadcast variants superseded by
  their Low/High counterparts (broadcastExclude,
  broadcastToDMParticipants(+Exclude), sendSequencedToUsers,
  PubSub.debugDump). Test references were comments only; updated to
  name the live variants.
- Separate 'Phase X Step Y' file headers from the package clause with a
  blank line so staticcheck ST1000 no longer reads them as malformed
  package comments (proper package docs exist in hub.go/manifest.go).
- Add .gitattributes normalizing line endings to LF on checkout —
  the Windows CI runner materialized CRLF, which made every
  prettier-formatted file fail the format gate.

Known remainder (pre-existing, out of P0 scope): golangci-lint with
-tags wazero reports 3 gosec + 2 staticcheck and -tags otel 1+1; CI
lints the default build. Tracked for the P1 plugin pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Server/plugin/loader.go

@@ -13,6 +13,7 @@
 //
 // Loader walks the directory, parses every plugin.json, and returns a slice
 // of foundPlugin records. The Registry then persists each into the store.
+
 package plugin
 
 import (