PowerTree v0.9.0

The "most useful and user-friendly" release — implements the competitive
audit vs. LTpowerPlanner (docs/AUDIT-2026-08-08-competitive.md), keeping
everything deliberately small.

• SI-suffix value entry everywhere: type 100m, 4.7u, 2.2k,
  50 mΩ in any electrical field; engineering-notation display; invalid
  input flags red instead of silently mangling.
• Cost + board-area fields (optional, per element) with per-tree
  rollups in the executive summary, HTML report, Excel, CLI and library
  parts — the LTpowerPlanner comparison axes, vendor-neutral.
• Compare architectures (Project menu, Ctrl+Shift+A; CLI compare;
  MCP tool): every tree side by side on power, efficiency, loss, cost,
  area, growth capacity and findings.
• PMIC modelling pattern: Quad-output PMIC template + user-guide
  section — one block, one converter per rail, shared refdes and Iq;
  electrically exact for DC budgeting without a DAG rewrite.
• Gesture polish: clickable datasheet links (↗), F2 / double-click
  rename, double-click a block outline to collapse (and a summary node to
  expand), first-run empty-canvas hint.

Explicit non-changes (per the audit's no-over-engineering rule): no SPICE,
no vendor part database, no cloud, no DAG, no UI modes.