docs: resync after card fixes — title auto-fit, truncate, abbreviated ticks (#15)

Several recent code changes hadn't propagated to the docs:

- design-guidelines
  * Card frame title row: document the 11–15 px auto-shrink (not a flat
    15 px anymore).
  * Donut Top-N: already 7 (updated earlier).
  * Bar-chart section renamed to cover weekday + by-year too; document
    the peak-vs-dim highlight convention and the niceTicks yMax ≥ max
    invariant.
  * Add Heatmap / Stat-column (streak) / List (top-starred) card
    sections — they were missing entirely.
  * Rewrite "Text overflow" from "we don't truncate" to the current
    truth (truncate helper, formatTick abbreviations).
  * Replace dangling `truncateName` reference with `truncate`.

- code-standards
  * SVG output standards: call out truncate, formatTick abbreviation,
    header auto-fit so the card-review gate reflects what the renderers
    actually do.

- codebase-summary
  * Layout tree: svg.go / axis.go comments list the helpers they now
    contain; productive.go notes the weekday histogram.
  * demo/ tree shows the index vs per-theme split.
  * Data-flow diagram includes Weekday in the productive pass.
  * Test coverage row lists TestCardsFitFrame / TestFitTitleFontSize /
    TestNiceTicksCoversMax — the new invariant guards.

- system-architecture
  * Shared primitives list adds renderWeekday and renderHeatmap; donut
    blurb updated to "top 7".
  * New "Chart-geometry invariants" block documents niceTicks ceiling,
    formatTick abbreviation, header auto-fit.

- project-roadmap
  * Phase 7.5 bullet updated to describe the index + per-theme demo
    split (was single-README TOC).

docs/code-standards.md

@@ -57,8 +57,10 @@ Never write comments that describe what well-named code does (`// increment coun
 ## SVG output standards
 
 - Always XML-escape user-controlled strings through `escapeXML` (`&`, `<`, `>`, `"`, `'`).
-- Numbers formatted via `formatInt` with thousands separators.
+- Long user-controlled strings (bio, names, company, repo slugs) go through `truncate` in `svg.go` before rendering — never print raw multi-line input that could push a later element off-screen.
+- Body numbers formatted via `formatInt` (thousands separators). Y-axis tick numbers go through `formatTick`, which abbreviates ≥ 1000 to `k` / `M` / `B` so no label exceeds 4 chars.
 - Stable viewbox per card (`340×200`) matching github-profile-summary-cards.
+- Titles render through `header()` which auto-shrinks font-size (15 → 11 px) when the string wouldn't fit in `width − 20 − 4`.
 - No `<script>` tags, no event handlers. Cards are pure markup.
 
 ## Testing