feat(books): add Learning Shapes with Squish, rebuild printables PDF, simplify signup email

[konjoinfinity]

Summary

• Adds Learning Shapes with Squish as a fifth book card on the squish.run/books site, with its real cover art and Amazon link (a.co/d/0fzbFoD7), and adjusts the book grid from a 4-up to a 3-up layout at wide viewports.
• Rebuilds the free coloring-pages PDF (docs/books/downloads/squish-lilyan-coloring-pages.pdf) from the four Squish & Lilyan coloring-page illustrations, replacing the previous 2-page PDF with a 4-page one, letter-sized and print-ready.
• Replaces the Buttondown ESP integration in functions/api/subscribe.js with a simpler Resend-based notification: each email signup on the site is forwarded straight to wes@squish.run (subject/body includes the submitted email and src attribution tag) instead of requiring a full mailing-list account. Requires a RESEND_API_KEY env var in the Cloudflare Pages project (not committed).
• Updates related copy/comments on the page (book count, success message, integration docs) to match.

Type of change

• New feature
• Bug fix
• Performance improvement
• Documentation update
• Refactor / cleanup

Checklist

• Changes are scoped to one logical concern (the books microsite, not the inference server)
• No hardcoded absolute paths
• No model weights, eval output, or log files staged
• pytest tests/ — n/a, no Python changes
• ruff check — n/a, no Python changes

Related issues

None.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KRmTJECM7bksNeJ3FUjqQw

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[konjoinfinity]

G4 · Complexity + Size + DRY is red on this PR, but it's not caused by this diff — this PR only touches docs/books/index.html, docs/books/downloads/squish-lilyan-coloring-pages.pdf, docs/books/assets/covers/shapes.jpg, and functions/api/subscribe.js; no Python files. The failure is the same one already on main HEAD (40b3ec7, run 31738617400): the complexity ratchet (147 functions above grade C) and squish/backend.py at 511 lines (not in .konjo/oversized-allowlist.txt). No fix for it exists yet in an open PR — #227 is a separate, unrelated konjo-gates onboarding effort, not a fix for this ratchet. Standing down on this check for this PR; will keep watching for CI on the rest of the checks and any review feedback.

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[konjoinfinity]

Test Linux (Python 3.11) and Test Linux (Python 3.12) are also red on this PR (tests/test_wave120_dead_global_purge.py::test_server_line_count_under_threshold), also not caused by this diff — squish/server.py is untouched by this PR (git diff origin/main -- squish/server.py is empty; byte-identical to main).

Root cause: the test computes line_count = server_text.count('\n') + 1, which over-counts by one for any file ending in a trailing newline (the normal case) — server.py has 6399 actual lines but this formula yields 6400, tripping the < 6400 ceiling with assert 6400 < 6400. Since the file content is unchanged from main, this same assertion fails identically there too; not something introduced by this PR, and not something a docs-site PR should be fixing. Standing down on these two checks as well.

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Generated by Claude Code

[konjoinfinity]

Test (Python 3.11), Test (Python 3.12), and Test (Python 3.13) (macOS) are also red, again not from this diff — the additional failures beyond the server.py line-count issue already covered above are 3 bfloat16/PEP-3118 numpy buffer errors in tests/test_block_kv_cache_coverage.py and tests/test_prompt_kv_cache_coverage.py, in squish/kv/block_kv_cache.py / squish/kv/prompt_kv_cache.py — files this PR doesn't touch.

Verified pre-existing: main's own latest CI run (31738617407, head 40b3ec7) shows the identical failure pattern — every Python test job red (Test (Python 3.11/3.12/3.13), Test Linux (Python 3.11/3.12), Test Rust extension), same jobs, same shape. This is a standing environment/numpy-version issue on main, not something introduced here. Standing down; nothing further to push on this docs-only PR for these.

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