docs: trim removed v3 provider apps from server-change area lists

Devin/CodeRabbit flagged that the .server-changes area enum still listed
coordinator/kubernetes-provider/docker-provider in CONTRIBUTING.md, the
.server-changes README, and the server-apps rule file.

Author: nicktrn

.claude/rules/server-apps.md

@@ -5,7 +5,7 @@ paths:
 
 # Server App Changes
 
-When modifying server apps (webapp, supervisor, coordinator, etc.) with **no package changes**, add a `.server-changes/` file instead of a changeset:
+When modifying server apps (webapp, supervisor, etc.) with **no package changes**, add a `.server-changes/` file instead of a changeset:
 
 ```bash
 cat > .server-changes/descriptive-name.md << 'EOF'
@@ -18,6 +18,6 @@ Brief description of what changed and why.
 EOF
 ```
 
-- **area**: `webapp` | `supervisor` | `coordinator` | `kubernetes-provider` | `docker-provider`
+- **area**: `webapp` | `supervisor`
 - **type**: `feature` | `fix` | `improvement` | `breaking`
 - If the PR also touches `packages/`, just the changeset is sufficient (no `.server-changes/` needed).

.server-changes/README.md

@@ -1,6 +1,6 @@
 # Server Changes
 
-This directory tracks changes to server-only components (webapp, supervisor, coordinator, etc.) that are not captured by changesets. Changesets only track published npm packages — server changes would otherwise go undocumented.
+This directory tracks changes to server-only components (webapp, supervisor, etc.) that are not captured by changesets. Changesets only track published npm packages — server changes would otherwise go undocumented.
 
 ## When to add a file
 
@@ -31,7 +31,7 @@ Speed up batch queue processing by removing stalls and fixing retry race
 
 ### Fields
 
-- **area** (required): `webapp` | `supervisor` | `coordinator` | `kubernetes-provider` | `docker-provider`
+- **area** (required): `webapp` | `supervisor`
 - **type** (required): `feature` | `fix` | `improvement` | `breaking`
 
 ### Description

CONTRIBUTING.md

@@ -281,7 +281,7 @@ EOF
 ```
 
 **Fields:**
-- `area` (required): `webapp` | `supervisor` | `coordinator` | `kubernetes-provider` | `docker-provider`
+- `area` (required): `webapp` | `supervisor`
 - `type` (required): `feature` | `fix` | `improvement` | `breaking`
 
 The body text (below the frontmatter) is a one-line description of the change. Keep it concise — it will appear in release notes.