fix(docs): remove stale hardcoded function count from Learn page

[hhimanshu]

Summary

• Removed the hardcoded 484 function count from content/docs/learn/(foundations)/functions.mdx — the intro paragraph now says TrueCalc implements "a wide range" of functions and links to the full function catalogue for the current count.
• The closing "Discovering functions from code" section similarly drops the stale "all 484 functions" phrasing in favor of "the complete function catalogue," which already links to the generated Reference tab.

How to test

• npm run dev, then open http://localhost:3000/docs/learn/foundations/functions (adjust base path if running without NEXT_PUBLIC_BASE_PATH).
• Confirm the intro paragraph reads "...implements a wide range of Google Sheets functions..." with a link to /reference/functions, and no hardcoded number appears anywhere on the page (search the rendered page for "484" — zero matches).
• Or without a server: grep -n 484 "content/docs/learn/(foundations)/functions.mdx" returns nothing.

Review

• Independent review: clean (reviewer: fresh subagent). Confirmed the diff touches only functions.mdx, content/docs/reference/functions/ is untouched, npm run build and npm run test-docs both pass (66/66 example blocks), and no other stale "484" references were introduced by this change (pre-existing occurrences in formulas.mdx and values-and-types.mdx are out of scope for this issue).

Test plan

• npm run build — static export succeeds, no errors
• npm run test-docs — 66/66 example blocks pass
• git diff --exit-code -- content/docs/reference/functions — clean, confirms generated reference docs untouched

closes #50

🤖 Generated with Claude Code

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