feat(local-model): a memory map and real colour in the chooser, the button first

The owner's verdict on the chooser: nice, but not nice enough, too much just
blue. He also wants "Run a local model" on top of the start screen, above
Run Claude Code.

The memory bar is now a map: the model, its context and the brief peaks side
by side on the track of what this Mac can give a model, each with its size in
a legend, and the verdict on the fit beside the figure. recommend() sends what
the need is made of as `Candidate.memory`.

Colour now carries meaning: green for good and tested, amber for tight, orange
for slow, teal for the context. Violet is the feature's own colour, on its
start screen button and its main action. Every row has a size tile and a speed
gauge scaled to the fastest row in the list. The light skins get deeper values
of the same colours, and the window is 40 px taller to hold it without
scrolling.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/types/local-model.ts

@@ -481,6 +481,12 @@ export interface Candidate {
   needBytes: number;
   /** `needBytes` as decimal GB text, no unit. */
   needGb: string;
+  /**
+   * What `needBytes` is made of, for the chooser's memory map: the model (`bytes +
+   * overheadBytes`), its context in use (`heldBytesPerToken * context`) and the brief peaks
+   * (`peakExtraBytes`). The three add up to `needBytes`.
+   */
+  memory?: { modelBytes: number; contextBytes: number; peakBytes: number };
   /** The model download in bytes (`LocalModelEntry.bytes`). */
   downloadBytes: number;
   /** `downloadBytes` as decimal GB text, no unit. */