address review feedback: portability, docs, and security hardening

- Replace grep -qP with POSIX-compatible LC_ALL=C grep -q '[^[:print:]]'
- Inline auth headers directly in curl calls (eliminate AUTH_HEADER variable)
- Remove redundant sys.exit(1) from Python for-else (shell empty-check suffices)
- Update top-of-file comment to match actual detection mechanism
- Remove -L from Gitea download curl calls to prevent auth header forwarding
  on potential redirects (defense-in-depth)

.gitea/actions/review/action.yml

@@ -1,7 +1,8 @@
 # This composite action supports both Gitea Actions and GitHub Actions runners.
-# It detects the VCS host type using the github.api_url context (set only on
-# GitHub/GHES runners) and uses the appropriate releases API for version
-# resolution and binary download (REST API on GitHub, direct URLs on Gitea).
+# It detects the VCS host type by checking whether github.api_url is set
+# (present on GitHub.com and GHES runners, absent on Gitea runners) and uses
+# the appropriate releases API for version resolution and binary download
+# (REST API on GitHub, direct URLs on Gitea).
 #
 # Security notes:
 # - On GitHub/GHES (VCS_TYPE=github), inputs.gitea-url is IGNORED to prevent
@@ -198,7 +199,7 @@ runs:
 
         # Validate token contains no control characters (defense-in-depth against header injection)
         if [ -n "$ACTION_TOKEN" ]; then
-          if printf '%s' "$ACTION_TOKEN" | grep -qP '[\x00-\x1f\x7f]'; then
+          if printf '%s' "$ACTION_TOKEN" | LC_ALL=C grep -q '[^[:print:]]'; then
             echo "Error: ACTION_TOKEN contains control characters" >&2
             exit 1
           fi
@@ -214,20 +215,17 @@ runs:
             API_URL="${SERVER_URL}/api/v1/repos/${ACTION_REPO}/releases?limit=1"
           fi
 
-          # Build auth header if token is available
-          AUTH_HEADER=""
+          # Fetch latest version with inline auth header (no intermediate variable)
           if [ -n "$ACTION_TOKEN" ]; then
             if [ "$VCS_TYPE" = "github" ]; then
-              AUTH_HEADER="Authorization: Bearer ${ACTION_TOKEN}"
+              VERSION=$(curl -sSf --connect-timeout 10 --max-time 30 \
+                -H "Authorization: Bearer ${ACTION_TOKEN}" "$API_URL" \
+                | python3 -c "import sys, json; releases = json.load(sys.stdin); print(releases[0]['tag_name'] if releases else '')")
             else
-              AUTH_HEADER="Authorization: token ${ACTION_TOKEN}"
+              VERSION=$(curl -sSf --connect-timeout 10 --max-time 30 \
+                -H "Authorization: token ${ACTION_TOKEN}" "$API_URL" \
+                | python3 -c "import sys, json; releases = json.load(sys.stdin); print(releases[0]['tag_name'] if releases else '')")
             fi
-          fi
-
-          if [ -n "$AUTH_HEADER" ]; then
-            VERSION=$(curl -sSf --connect-timeout 10 --max-time 30 \
-              -H "$AUTH_HEADER" "$API_URL" \
-              | python3 -c "import sys, json; releases = json.load(sys.stdin); print(releases[0]['tag_name'] if releases else '')")
           else
             VERSION=$(curl -sSf --connect-timeout 10 --max-time 30 "$API_URL" \
               | python3 -c "import sys, json; releases = json.load(sys.stdin); print(releases[0]['tag_name'] if releases else '')")
@@ -307,8 +305,6 @@ for a in assets:
     if a['name'] == '${BINARY}':
         print(a['id'])
         break
-else:
-    sys.exit(1)
 ")
           if [ -z "$BINARY_ASSET_ID" ]; then
             echo "Error: could not find asset '${BINARY}' in release ${VERSION}" >&2
@@ -322,8 +318,6 @@ for a in assets:
     if a['name'] == 'checksums.txt':
         print(a['id'])
         break
-else:
-    sys.exit(1)
 ")
           if [ -z "$CHECKSUMS_ASSET_ID" ]; then
             echo "Error: could not find asset 'checksums.txt' in release ${VERSION}" >&2
@@ -354,20 +348,22 @@ else:
           fi
         else
           # Gitea: Direct download via web release URLs (Gitea serves assets
-          # directly and supports token auth on these URLs)
+          # directly without redirects — no -L needed).
+          # SECURITY: Omitting -L prevents forwarding Authorization header to
+          # unexpected hosts if Gitea ever introduces CDN redirects.
           DOWNLOAD_URL="${SERVER_URL}/${ACTION_REPO}/releases/download/${VERSION}"
 
           if [ -n "$ACTION_TOKEN" ]; then
-            curl -sSfL --connect-timeout 10 --max-time 120 \
+            curl -sSf --connect-timeout 10 --max-time 120 \
               -H "Authorization: token ${ACTION_TOKEN}" \
               "${DOWNLOAD_URL}/${BINARY}" -o "${{ runner.temp }}/review-bot"
-            curl -sSfL --connect-timeout 10 --max-time 30 \
+            curl -sSf --connect-timeout 10 --max-time 30 \
               -H "Authorization: token ${ACTION_TOKEN}" \
               "${DOWNLOAD_URL}/checksums.txt" -o "${{ runner.temp }}/checksums.txt"
           else
-            curl -sSfL --connect-timeout 10 --max-time 120 \
+            curl -sSf --connect-timeout 10 --max-time 120 \
               "${DOWNLOAD_URL}/${BINARY}" -o "${{ runner.temp }}/review-bot"
-            curl -sSfL --connect-timeout 10 --max-time 30 \
+            curl -sSf --connect-timeout 10 --max-time 30 \
               "${DOWNLOAD_URL}/checksums.txt" -o "${{ runner.temp }}/checksums.txt"
           fi
         fi