ci: set least-privilege GITHUB_TOKEN permissions (#104)

Add top-level `permissions: contents: read` to every workflow. Without
it, jobs inherit the repo-default token scope (often read-write), so a
malicious dependency executing during install/build/test on a push to
the default branch would hold a write-capable token. Read-only by
default denies that; the publish job keeps its own job-level
`id-token: write` block (job-level permissions override the top-level
default), so trusted-publishing is unaffected.

Complements the SHA-pinning: pinning stops untrusted code from running;
this limits what it can do if it runs anyway. Fork-PR tokens are already
forced read-only by GitHub; this closes the push-triggered path.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Technologicat

.github/workflows/ci.yml

@@ -13,6 +13,9 @@ on:
     branches: [ master ]
   workflow_dispatch:
 
+permissions:
+  contents: read
+
 jobs:
   lint:
     runs-on: ubuntu-latest

.github/workflows/coverage.yml

@@ -10,6 +10,9 @@ on:
     branches: [ master ]
   workflow_dispatch:
 
+permissions:
+  contents: read
+
 jobs:
   codecov: