fix(prd-7): M1 architecture review — consolidate duplication, fix bugs, memoize detection

- F1: Consolidated updateForgejoCommentBody into unified updateCommentBody (~150 lines removed)
- F2: Fixed wrong run identifier in update-with-branch.ts (context.runId → getForgejoRunIndex())
- F3: Memoized detectPlatform() with _resetPlatformCache() for tests
- F4: Added getServerUrl() runtime helper to resolve constant-vs-function inconsistency
- F5: Fixed sticky comment bot matching on Forgejo via context.inputs.botName
- F6: Documented GHES heuristic misidentification in docs/forgejo.md
- Updated PRD M1 checkbox to complete

Progress: 17% complete — M1 done, M2 (error handling review) next

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/m7-integration.test.ts

@@ -9,7 +9,7 @@
  */
 
 import { describe, it, expect, beforeEach, afterEach } from "bun:test";
-import { detectPlatform } from "../src/platform/detector";
+import { detectPlatform, _resetPlatformCache } from "../src/platform/detector";
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -40,11 +40,13 @@ function restoreEnv() {
 
 describe("M7: Platform routing for mode handlers", () => {
   beforeEach(() => {
+    _resetPlatformCache();
     saveEnv("PLATFORM", "FORGEJO", "GITHUB_SERVER_URL");
   });
 
   afterEach(() => {
     restoreEnv();
+    _resetPlatformCache();
   });
 
   describe("detectPlatform() — used by tag mode and update-comment-link", () => {
@@ -156,13 +158,13 @@ describe("M7: Forgejo PR compare URL format", () => {
 // update-comment-link: platform-aware final comment body
 // ---------------------------------------------------------------------------
 
-describe("M7: updateForgejoCommentBody vs updateCommentBody", () => {
-  it("Forgejo version strips Unicode spinner", async () => {
-    const { updateForgejoCommentBody } = await import(
-      "../src/forgejo/comment-logic"
+describe("M7: unified updateCommentBody handles both platforms", () => {
+  it("strips Unicode spinner (Forgejo format)", async () => {
+    const { updateCommentBody } = await import(
+      "../src/github/operations/comment-logic"
     );
 
-    const result = updateForgejoCommentBody({
+    const result = updateCommentBody({
       currentBody:
         "Claude Code is working… ⏳\n\nI'll analyze this and get back to you.\n\n[View job run](https://git.wxs.ro/owner/repo/actions/runs/123)",
       actionFailed: false,