Feat: implement CTB/STB plot style table with PDF export integration

- src/io/plot_style.rs: PlotStyleTable and PlotStyleEntry data structures;
  CTB reader (deflate/zlib decompressed text format) with ACI→RGB and
  ACI→lineweight lookup; CTB writer (zlib compressed); LW_TABLE constant
- src/io/pdf_export.rs: accept optional PlotStyleTable; apply ACI color
  and lineweight overrides during PDF rendering
- src/scene/wire_model.rs: add `aci: u8` field to carry ACI index
- src/scene/render.rs: render_style() now returns ACI alongside RGBA
- src/scene/mod.rs + tessellate.rs: propagate aci through wire building
- app: PlotStyleLoad/Loaded/Clear messages and handlers;
  PLOTSTYLE LOAD | CLEAR | STATUS command; active_plot_style state on H7CAD
- flate2 added as dependency

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scene/wire_model.rs

@@ -44,6 +44,8 @@ pub struct WireModel {
     pub pattern: [f32; 8],
     /// Rendered line width in screen pixels (half-width = line_weight_px / 2).
     pub line_weight_px: f32,
+    /// ACI color index (1-255).  0 means true-color or unknown (no CTB lookup).
+    pub aci: u8,
     /// Pre-baked snap candidates (Center, Node, Quadrant, Insertion).
     pub snap_pts: Vec<(glam::Vec3, SnapHint)>,
     /// Per-segment tangent geometry for Tangent snap.
@@ -67,6 +69,7 @@ impl WireModel {
             points,
             color,
             selected,
+            aci: 0,
             pattern_length: 0.0,
             pattern: [0.0; 8],
             line_weight_px: 1.0,