docs: rewrite article in human voice, add mermaid diagrams

Full rewrite of ARTICLE.md applying a style guide derived from Nadh's blog
(nadh.in) and OneUptime. All data, tables, numbers, and references preserved.

Style changes:
  - Killed all em-dashes (was 80+, now 0). Replaced with commas, periods,
    or parentheses as appropriate.
  - Killed the "**Bold lead.** Followup sentence." pattern across all sections.
  - Killed the "**Question**: ... **Answer**: ..." structure.
  - Cut "Furthermore / Moreover / Additionally / However" entirely.
  - Cut "It's important to note that" and similar AI tells.
  - Section titles now assertions and questions, not noun phrases
    ("Your ORM is the bottleneck", "When to throw the ORM out").
  - First-person voice throughout. The narrator owns the result.
  - Inline code comments replace surrounding prose for PRAGMA blocks.
  - Mixed sentence lengths: long thinking sentences alongside punchy ones.

Added 4 Mermaid diagrams:
  1. ORM stack (7 layers, red-highlighted overhead) → SQLite engine.
  2. Raw stack (2 layers) → SQLite engine.
  3. Connection architecture (writer pool 1 + reader pool N → WAL DB).
  4. Decision flowchart for "when to throw the ORM out".

Article shape: 667 → 650 lines. 62 → 64 external links. 4 mermaid blocks.

Author: Tanay10x