fix(action): detect VCS host type for version resolution and binary download

The composite action hardcoded Gitea-specific API paths and repo references
that broke when running on GitHub Enterprise Server.

Changes:
- Add 'action-repo' input to specify the repo hosting review-bot releases,
  separate from the 'repo' input (which is the target repo being reviewed)
- Auto-detect action repo from github.action_repository context variable,
  falling back to 'rodin/review-bot' for backward compatibility
- Detect VCS host type (Gitea vs GitHub) from server URL using hostname
  heuristic (URLs containing 'github' use /api/v3/, others use /api/v1/)
- Pass computed server_url and action_repo between steps via GITHUB_OUTPUT
  to avoid redundant computation
- Update descriptions to be host-agnostic

Fixes #120

.gitea/actions/review/action.yml

@@ -1,17 +1,21 @@
-# This composite action is designed for Gitea Actions runners.
-# Gitea Actions supports GitHub Actions syntax including $GITHUB_OUTPUT,
-# actions/cache, and actions/checkout.
+# This composite action supports both Gitea Actions and GitHub Actions runners.
+# It detects the VCS host type (Gitea vs GitHub) from the server URL and uses
+# the appropriate releases API format for version resolution and binary download.
 # Requirements: python3, sha256sum, curl (all present on ubuntu-* runners).
 name: 'AI Code Review'
 description: 'Run AI-powered code review on a pull request using review-bot'
 
 inputs:
   gitea-url:
-    description: 'Gitea instance URL (defaults to server_url)'
+    description: 'VCS instance URL (defaults to server_url). Works for both Gitea and GitHub.'
     required: false
     default: ''
   repo:
-    description: 'Repository (owner/name, defaults to current)'
+    description: 'Repository to review (owner/name, defaults to current)'
+    required: false
+    default: ''
+  action-repo:
+    description: 'Repository hosting review-bot releases (owner/name). Defaults to github.action_repository or rodin/review-bot.'
     required: false
     default: ''
   pr-number:
@@ -19,7 +23,7 @@ inputs:
     required: false
     default: ''
   reviewer-token:
-    description: 'Gitea token for posting the review'
+    description: 'Token for posting the review'
     required: true
   reviewer-name:
     description: 'Display name for the reviewer'
@@ -112,19 +116,50 @@ runs:
       id: version
       shell: bash
       run: |
-        GITEA_URL="${{ inputs.gitea-url || github.server_url }}"
-        REPO="${{ inputs.repo || 'rodin/review-bot' }}"
+        SERVER_URL="${{ inputs.gitea-url || github.server_url }}"
+        # Strip trailing slash if present
+        SERVER_URL="${SERVER_URL%/}"
+
+        # Determine the repo hosting review-bot releases (not the repo being reviewed)
+        ACTION_REPO="${{ inputs.action-repo }}"
+        if [ -z "$ACTION_REPO" ]; then
+          # github.action_repository is the repo containing the running action
+          ACTION_REPO="${{ github.action_repository }}"
+        fi
+        if [ -z "$ACTION_REPO" ]; then
+          # Final fallback for Gitea (which may not set action_repository)
+          ACTION_REPO="rodin/review-bot"
+        fi
+
+        # Detect VCS host type from server URL
+        # GitHub/GHES URLs contain "github" in the hostname
+        if echo "$SERVER_URL" | grep -qi "github"; then
+          VCS_TYPE="github"
+        else
+          VCS_TYPE="gitea"
+        fi
+
         if [ "${{ inputs.version }}" = "latest" ]; then
-          VERSION=$(curl -sSf "${GITEA_URL}/api/v1/repos/${REPO}/releases?limit=1" \
+          if [ "$VCS_TYPE" = "github" ]; then
+            # GitHub REST API (GHES uses /api/v3/, github.com uses /api/v3/ too)
+            API_URL="${SERVER_URL}/api/v3/repos/${ACTION_REPO}/releases?per_page=1"
+          else
+            # Gitea API
+            API_URL="${SERVER_URL}/api/v1/repos/${ACTION_REPO}/releases?limit=1"
+          fi
+
+          VERSION=$(curl -sSf "$API_URL" \
             | python3 -c "import sys, json; releases = json.load(sys.stdin); print(releases[0]['tag_name'] if releases else '')")
           if [ -z "$VERSION" ]; then
-            echo "Failed to determine latest version" >&2
+            echo "Failed to determine latest version from ${API_URL}" >&2
             exit 1
           fi
         else
           VERSION="${{ inputs.version }}"
         fi
         echo "version=${VERSION}" >> "$GITHUB_OUTPUT"
+        echo "action_repo=${ACTION_REPO}" >> "$GITHUB_OUTPUT"
+        echo "server_url=${SERVER_URL}" >> "$GITHUB_OUTPUT"
 
     - name: Cache review-bot binary
       id: cache
@@ -137,14 +172,16 @@ runs:
       if: steps.cache.outputs.cache-hit != 'true'
       shell: bash
       run: |
-        GITEA_URL="${{ inputs.gitea-url || github.server_url }}"
-        REPO="${{ inputs.repo || 'rodin/review-bot' }}"
+        SERVER_URL="${{ steps.version.outputs.server_url }}"
+        ACTION_REPO="${{ steps.version.outputs.action_repo }}"
         VERSION="${{ steps.version.outputs.version }}"
         BINARY="review-bot-linux-amd64"
 
-        curl -sSfL "${GITEA_URL}/${REPO}/releases/download/${VERSION}/${BINARY}" \
+        # Download URL format is the same on both Gitea and GitHub:
+        # {server}/{owner}/{repo}/releases/download/{tag}/{asset}
+        curl -sSfL "${SERVER_URL}/${ACTION_REPO}/releases/download/${VERSION}/${BINARY}" \
           -o "${{ runner.temp }}/review-bot"
-        curl -sSfL "${GITEA_URL}/${REPO}/releases/download/${VERSION}/checksums.txt" \
+        curl -sSfL "${SERVER_URL}/${ACTION_REPO}/releases/download/${VERSION}/checksums.txt" \
           -o "${{ runner.temp }}/checksums.txt"
 
         # Verify SHA-256 checksum