M8.18: Blend Options dialog and the Blend tool's anchor targeting

[bflatastic]

Blend Options is now a real dialog, and the Blend tool can blend from chosen anchor points and add keys to an existing blend.

M8.18: Blend Options dialog and Blend tool

• Blend Options opens a dedicated dialog (blendOptions, ui.blendOptions):
  • Spacing dropdown with its value, the Align to Page / Align to Path buttons, and live preview.
  • Prefilled from the selected blend. Before, OK silently turned a Smooth Color blend into 5 steps.
  • With nothing selected, it sets the defaults new blends start with (Prefs.blend_options).
  • New query: object.blend.info.
• Blend tool:
  • The anchor points you click become the blend's start points. This adds BlendSpec.starts (append-only) and object.blend.make {starts}, and the path interpolation uses them.
  • Clicking a blend and then another object adds a key instead of nesting a blend inside a blend. Make does the same when a blend is selected.
  • Double-click on the canvas, Alt-click, or a double-click on the toolbar button opens Blend Options.
  • New hint text and 3 new cursors.
• Blend evaluation moved to the new crates/doc/src/blend.rs. live.rs re-exports the old API, and each pair of keys is now prepared once per blend.
• The ROADMAP's M8 row lists this change.

Checks

• Last of a five-PR stack (M8.5 → M8.3 → M8.9 → M8.12 → M8.18) on main at 5a93e78 (M8.16: Enveloped type exports distorted, run by run, everywhere #184). The agent rebased it onto M8.15 itself: the two options_json became blend_options_json and envelope_options_json, and both behaviours are kept. Stacking conflicts in shared lists and docs were merged token by token, keeping both sides.
• cargo xtask ci passes all 7 steps (fmt, clippy, tests, assets, brands, layers, wasm) on the top of the stack, with 3,164 tests.
• Nothing dropped. One deliberate change: the Blend Options… menu row no longer carries {"steps": 5}. It keeps the same label and id and opens the new dialog. object.blend.options also works with no blend selected, to set the defaults.

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