feat(image-editor): Note + Frame + Path Selection + recover Hand/Fullscreen fix

[lyfuci]

Summary

Round out the PS palette with three more functional tools, plus recover the focus-button + Hand-tool fix that didn't make it into PR #44 (the commit landed after the merge cut).

New tools

• Note (N) — click to drop a sticky-note marker. New `NoteShape` renders as a 16-px folded-corner pentagon with a one-line preview label below. Notes are gated on `liveCanvas`, so they appear on screen but never bake into PNG / JPEG / WebP exports — they're a pure annotation aid.
• Frame — drag a rectangle to place a placeholder frame. New `FrameShape` renders as a dashed grey rect with a diagonal X across it (PS Frame Tool's empty-frame visual). Resizable via the standard 4 corner handles. Visible in export.
• Path Selection (A) — un-stubbed and aliased to the Move tool's pick-and-move behaviour. Until the Pen tool ships, it functions identically to the no-tool selection arrow; full anchor-level path selection follows when vectors land.

These three tools were registered in `STUB_TOOLS` and the `Tool` type union but had never been rendered in the palette. This PR adds the palette entries (with PS-aligned icons: `StickyNote`, `LayoutTemplate`, `MousePointer`) and wires the full implementation.

Bundled UX fix (recovered from PR #44)

The focus-button + Hand-tool wiring commit landed on the branch after the merge cut, so it never reached main. Cherry-picked here:

• F shortcut unbound (Photoshop's F cycles screen modes — keeping our F bound to focus-mode collided with muscle memory).
• Green Fullscreen button in the tab strip's right corner (turns red when active, indicating "click to exit").
• Hand tool (H) is no longer a stub — selecting it puts the editor into pan mode (same as holding Space).

State + render changes

• types.ts: `NoteShape` + `FrameShape` added to the `Shape` union. `Project` files round-trip both via the existing `serializeProject` (no schema bump needed — the union is a tagged variant).
• drawing.ts: `drawNote` (sticky-note pentagon + folded-corner shadow + preview label) and `drawFrame` (dashed rect + diagonal X + optional name).
• hit.ts: bbox + (frame-only) corner handles. Note bbox covers the 16-px icon footprint so users can click to select it.
• transform.ts: translate covers both shapes; resize covers frame.
• render.ts: skips note layers in the layer loop when `!input.liveCanvas`.
• LayersPanel.tsx: `layerLabelKey` gains note + frame branches so the right-sidebar layer list shows readable names.

STUB_TOOLS shrinks

Before: spotHeal, stamp, historyBrush, pen, arrowPath, frame, note  (+ hand on main)
After:  spotHeal, stamp, historyBrush, pen

Pen is the next deep PR; spotHeal / stamp / historyBrush all share the "sample source pixels" infrastructure and will land together as the final palette PR.

Keyboard

• `A` → Path Selection
• `N` → Note
• `H` → Hand (now functional)
• `F` → unbound (was focus toggle)

Test plan

• Note (N): click → text prompt → sticky-note appears with preview label. Export PNG → note not present in exported file.
• Frame: drag a rect → dashed-X placeholder appears. Resize via corner handles. Export PNG → frame is present.
• Path Selection (A): click an existing layer → it selects + moves like the regular Move tool.
• Hand (H): cursor becomes grab; drag pans the canvas. Same as holding Space.
• F key does nothing.
• Green ⛶ Fullscreen button → UI hides; button turns red ⛶ Exit fullscreen. Click again or Esc to exit.
• Save .json → reload — notes + frames round-trip.
• Right sidebar layer list: notes show as "Note", frames show as "Frame".

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