v0.0.4.0 feat(module-2): tam giác đồng dạng (lớp 8, scale slider) (#4)

* feat(component): similarity-scale slider controller

Single-slider similarity demo for Module 2. Fixed △ABC, scaled △A'B'C' computed
each frame as `centroid_target + k · (vertex − centroid_ABC)` for k ∈ [0.5, 2].
The slider's input event is the only event listener — no Pointer Events here
(we're not dragging vertices in this MVP). AbortController teardown on
astro:before-swap as before.

The renderTicks helper is duplicated from congruence-sss.ts for now — when
Module 4 lands we'll factor it out into a shared module. Premature
abstraction would force a circular import structure for one helper.

* feat(module-2): tam giác đồng dạng (lớp 8) with scale slider

Page at /lop-8/tam-giac-dong-dang/. △ABC fixed on the left at scalene scale-72.8 / 83.2 / 93.4 sides. △A'B'C' is the runtime scaled image, controlled by a
single range input k ∈ [0.5, 2] step 0.05.

Live readout table shows all six side lengths and all three ratios. The killer
moment: drag the slider, watch all 3 ratios stay numerically equal to each
other (= 1/k). That equality IS the definition of similarity, made visible.

Tick marks per Decision D3: 1/2/3 ticks color-paired (#D7263D / #1B998B /
#F46036). Triangle 1 ticks rendered once on mount; triangle 2 ticks redrawn
on every slider input.

Hub: lớp 8 card flips to live status. All 3 grade cards now active —
the autoplan 3-module hero set is complete.

* chore: VERSION 0.0.4.0 + CHANGELOG + TODOS update

v0.0.4.0 = scaffold + Module 3 (góc nội tiếp) + Module 1 (tam giác bằng nhau)
+ Module 2 (tam giác đồng dạng). All three MVP modules from autoplan now live.

Move 2 P1 items to Completed (scale slider, ratio readout) and reduce Module 2
remaining items to P2 (free-drag mode) + P3 (numeric angle readouts).

---------

gstack/package.json

@@ -1,6 +1,6 @@
 {
   "name": "try-gstack",
-  "version": "0.0.3.0",
+  "version": "0.0.4.0",
   "private": true,
   "type": "module",
   "description": "Hình Học Sống — Interactive Vietnamese THCS geometry visualizer (lớp 7-9). Static site, drag-to-explore theorems.",