Fix code scanning and dependabot security alerts (#756)

* Fix code scanning and dependabot security alerts

Code scanning fixes (14 alerts):
- Fix XSS in OG image route by validating request origin against allowlist
- Fix incomplete URL sanitization in blog layout using exact hostname matching
- Bind port-check socket to 127.0.0.1 instead of 0.0.0.0
- Add explicit permissions to 7 GitHub Actions workflows

Dependabot fixes:
- Update @isaacs/brace-expansion 5.0.0 -> 5.0.1 (CVE-2026-25547)
- Update bytes 1.10.1 -> 1.11.1 (CVE-2026-25541)
- Update time 0.3.41 -> 0.3.47 (CVE-2026-25727)
- Update cryptography 45.0.7 -> 46.0.5 (CVE-2026-26007)
- Update python-multipart 0.0.20 -> 0.0.22 (CVE-2026-24486)
- Update urllib3 2.6.2 -> 2.6.3 in test lockfiles (CVE-2026-21441)
- Update Werkzeug 3.1.4 -> 3.1.5 (CVE-2026-21860)

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

* Address PR review feedback

- Replace plano.katanemo.com with planoai.dev in allowed hosts
- Add planoai.dev to OG route and blog layout allowlists
- Revert socket bind to 0.0.0.0 (intentional for port-in-use check)

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/docker-push-main.yml

@@ -8,6 +8,9 @@ on:
     branches:
       - main
 
+permissions:
+  contents: read
+
 jobs:
   # Build ARM64 image on native ARM64 runner.
   build-arm64:

.github/workflows/docker-push-release.yml

@@ -7,6 +7,9 @@ on:
   release:
     types: [published]
 
+permissions:
+  contents: read
+
 jobs:
   # Build ARM64 image on native ARM64 runner
   build-arm64:

.github/workflows/e2e_plano_tests.yml

@@ -6,6 +6,9 @@ on:
       - main
   pull_request:
 
+permissions:
+  contents: read
+
 jobs:
   e2e_plano_tests:
     runs-on: ubuntu-latest-m

.github/workflows/pre-commit.yml

@@ -5,6 +5,9 @@ on:
   push:
     branches: [main]
 
+permissions:
+  contents: read
+
 jobs:
   pre-commit:
     runs-on: ubuntu-latest

.github/workflows/rust_tests.yml

@@ -5,6 +5,9 @@ on:
   push:
     branches: [main]
 
+permissions:
+  contents: read
+
 jobs:
   test:
     name: Test

.github/workflows/static.yml

@@ -3,6 +3,9 @@ on:
   push:
     branches: [main]
 
+permissions:
+  contents: write
+
 jobs:
   build:
     runs-on: ubuntu-latest

.github/workflows/validate_plano_config.yml

@@ -6,6 +6,9 @@ on:
       - main
   pull_request:
 
+permissions:
+  contents: read
+
 jobs:
   validate_plano_config:
     runs-on: ubuntu-latest