feat: embed report JSON in HTML and update footer verify link + QR code

[gkanitz]

What to build

Make the HTML report self-describing and verifiable by embedding the full report JSON inside it, and update the footer to give readers a single click path to verify the report.

Three concrete changes:

1. Embed JSON in the HTML
Add a `reportJSON` template function to the render package that marshals the `report.Report` as JSON and injects it into `layout.tmpl` as:
```html

<script type="application/json" id="coderepute-report">{"schema_version":...}</script>

```
This replaces `report.json` as the machine-readable data carrier. The separate `report.json` file is no longer generated.

2. Add XMP meta tags to ``
```html


```
Headless Chromium preserves these in the PDF's XMP metadata, which the verify page reads for PDF uploads.

3. Update the footer

• Replace the existing hardcoded repo URL QR code with one generated from `.Verification.VerifyURL` (falls back to the base verify page URL when unverified)
• Add a text link: `Verify this report` alongside the QR code
• The footer should clearly communicate: "To verify this report, visit the link or scan the QR code and upload this file"

Acceptance criteria

• `report.html` contains `<script type="application/json" id="coderepute-report">` with the full report JSON
• `report.json` is no longer written to disk by the CLI
• `` and `` are present in ``
• Footer QR code points to `VerifyURL` (not the hardcoded GitHub repo URL)
• Footer contains a human-readable "Verify this report" link
• Golden file test updated; `go test ./...` passes

Blocked by

• feat: add verify_url field to Verification schema #33