refactor(card): shrink cards from 500x220 to 340x200

Two ghstats cards side-by-side at 500px overflow GitHub's README column
width (~816px). Matching github-profile-summary-cards' 340x200 lets
consumers place two cards per row cleanly.

- Shared header() rect corner radius 8→6, title font 18→15, title anchor
  (25,35)→(20,30).
- All card layouts reworked:
  * profile + stats: row padding 70→55 / 24→20, icon 14→12, value
    font 13→12, stats right-anchor x=475→320.
  * donut_chart: centre (380,120)→(250,110), outerR 70→55, innerR 38→30,
    legend y0 70→55, swatch 12→10, topN 6→5.
  * productive-time: leftAxis 50→35, topPad 60→45, barGap 2→1.
  * contributions: leftPad/rightPad 35→28, topPad 60→45, chartH 120→105.

Visual parity with github-profile-summary-cards; two-per-row layouts in
profile READMEs now fit.

Also: document the one-time GitHub Marketplace publishing step in
deployment-guide (no CLI flag exists — UI checkbox only).

docs/deployment-guide.md

@@ -110,7 +110,12 @@ runs:
 3. On green, GHCR push + cross-platform binary artifacts happen automatically.
 4. Docker base images and third-party actions are SHA-pinned (with version
    comments) so mutable-tag changes upstream can't rewrite a released image.
-5. Update any public Actions marketplace metadata if the major version changed.
+5. **Marketplace publishing (one-time per repo):** GitHub only exposes the
+   "Publish this Action to the GitHub Marketplace" toggle on the Release
+   web UI — there is no CLI flag. Open the newly created release at
+   `https://github.com/tiennm99/ghstats/releases/tag/vX.Y.Z/edit`, tick the
+   marketplace checkbox, accept the terms, and re-publish. Subsequent
+   releases inherit marketplace visibility automatically.
 
 ## Rollback