Add dynamic coverage badge from main branch (#18)

Update CI to extract coverage % on main pushes and store an
\�ndpoint.json\ on a \coverage-data\ branch (same pattern as
[Presidio](https://github.com/microsoft/presidio)). Update README badge
to use shields.io endpoint pointing to that branch.

### Changes
- **ci.yml**: Added 'Update coverage badge' step that runs on push to
main, extracts line coverage from \coverage-summary.json\, generates a
shields.io-compatible \�ndpoint.json\ with color coding, and pushes it
to the \coverage-data\ branch
- **README.md**: Updated coverage badge to use \shields.io/endpoint\
reading from the \coverage-data\ branch

### Notes
- No external services or secrets needed — uses the built-in
\GITHUB_TOKEN\
- \contents: write\ permission scoped only to the coverage job
- Badge color ranges: red (<45%) → yellow → yellowgreen → green →
brightgreen (≥90%)

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dorlugasigal

.github/workflows/ci.yml

@@ -29,6 +29,9 @@ jobs:
   coverage:
     name: Coverage
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
@@ -44,6 +47,23 @@ jobs:
           json-summary-path: coverage/coverage-summary.json
           json-final-path: coverage/coverage-final.json
           file-coverage-mode: all
+      - name: Update coverage badge
+        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+        run: |
+          COVERAGE=$(node -e "const c = require('./coverage/coverage-summary.json'); console.log(c.total.lines.pct)")
+          if (( $(echo "$COVERAGE >= 90" | bc -l) )); then COLOR="brightgreen"
+          elif (( $(echo "$COVERAGE >= 75" | bc -l) )); then COLOR="green"
+          elif (( $(echo "$COVERAGE >= 60" | bc -l) )); then COLOR="yellowgreen"
+          elif (( $(echo "$COVERAGE >= 45" | bc -l) )); then COLOR="yellow"
+          else COLOR="red"; fi
+          echo "{\"schemaVersion\":1,\"label\":\"coverage\",\"message\":\"${COVERAGE}%\",\"color\":\"${COLOR}\"}" > endpoint.json
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git fetch origin coverage-data:coverage-data 2>/dev/null || git checkout --orphan coverage-data
+          git checkout coverage-data
+          git add endpoint.json
+          git commit -m "Update coverage badge to ${COVERAGE}%" || true
+          git push origin coverage-data
 
   lint:
     name: Lint

README.md

@@ -4,7 +4,7 @@
 
 [![npm version](https://img.shields.io/npm/v/termbeam.svg)](https://www.npmjs.com/package/termbeam)
 [![CI](https://github.com/dorlugasigal/TermBeam/actions/workflows/ci.yml/badge.svg)](https://github.com/dorlugasigal/TermBeam/actions/workflows/ci.yml)
-[![Coverage](https://img.shields.io/badge/coverage-check%20PR-blue)](https://github.com/dorlugasigal/TermBeam/pulls)
+[![Coverage](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/dorlugasigal/TermBeam/coverage-data/endpoint.json)](https://github.com/dorlugasigal/TermBeam/actions/workflows/ci.yml)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 
 TermBeam lets you access your terminal from a phone, tablet, or any browser — no SSH, no port forwarding, no config files. Run one command and scan the QR code.