Adds "sidepanel" to the TabsProps variant union and scoped CSS that:
- disables the [data-slot="tabs-list"]::after flex-grow filler so the
  consumer's 40px right reserve stays flush against the panel edge
- neutralizes the base tabs-trigger-wrapper chrome (borders, bg, selected
  tint) so consumers can style triggers via Tailwind
- owns the color/bg/state contract on [data-slot="tabs-trigger"]:
  text-weak default, text-base selected, surface-raised-base selected bg,
  surface-base-hover on hover

Type-level test asserts the union accepts "sidepanel" (tsc gates the
regression; bun strips types at runtime so the test is a compile-time
check in practice).

- DEFAULT_RIGHT_PANEL_WIDTH=340, MIN=300, MAX=520 (exported)
- clampRightPanelWidth pure factory (exported for unit coverage)
- rightPanel seed { width: 340 } in createStore
- layout.rightPanel accessor with clamped width() memo and resize()

Persisted store round-trips existing layout.v6 keys; missing rightPanel
in legacy blobs falls back to the seed default, then clamp guards.

- Export pure formatRightPanelWidth(open, width) helper for unit coverage
- panelWidth now sources from layout.rightPanel.width() instead of
  calc(100% - session.width), so the panel stops growing with viewport
- Tabs root uses variant="sidepanel" (tabs.css scoped block handles the
  wrapper-chrome reset + trigger color/bg contract)
- 40px aria-hidden reserve div appended inside Tabs.List so the tab row
  has a right margin matching the design prototype

DOM-render tests sit outside bun's Solid-incompatible JSX transform; the
existing mock-to-null harness stays, with typecheck gating variant prop
type and Task 6 e2e gating the end-to-end width wiring.

…emos

With the right panel now self-sized via layout.rightPanel (Task 2-3),
the middle splitter that resized layout.session is a zombie. This commit:

- deletes desktopSidePanelOpen + sessionPanelWidth (no readers left)
- flips session column wrapper from "shrink-0 md:flex-none + inline
  style.width" to "min-w-0 flex-1" so it claims the gap between
  sidebar and right panel on all breakpoints
- removes the <Show when={desktopReviewOpen()}>...<ResizeHandle> block
  that drove layout.session.resize

size.active() still threads through (terminal panel + transition class
on the session column), size.start/touch still fire from the file-tree
handle inside Review tab; Task 5 adds the new left-edge handle that
also participates.

- Export makeRightPanelResizeHandler pure factory — touch-then-resize
  callback is unit-testable outside Solid's DOM.
- Mount a wrapper <div onPointerDown={size.start}> above the tab shell,
  with a ResizeHandle (edge="start", direction="horizontal") attached
  to the aside's left edge. min=300 max=520.
- Clamping stays centralized in layout.rightPanel.resize (Task 2), so
  the handler forwards the raw width straight through.

pointerdown + ResizeHandle prop binding are typecheck-gated; Task 6's
e2e drives the persist round-trip end-to-end.

- Expose the provider's layout object on window.__pawworkLayout under
  import.meta.env.DEV so e2e can drive layout.rightPanel.resize(n)
  without wiring a fake pointer-drag sequence.
- New spec at e2e/session/right-panel-width.spec.ts: open the panel
  via the titlebar toggle, set width to 400, reload, verify persisted.

Covers the unit gap where Task 5's mock doesn't exercise the real
Solid store + persisted() round-trip.

Per crosscheck codex P2: a malformed persisted blob or a buggy drag
math path could hand clampRightPanelWidth a NaN or ±Infinity, and
Math.max/Math.min would propagate that straight through to the style
width, producing "NaNpx" or "Infinitypx".

Treat non-finite like undefined — fall back to DEFAULT. Two new test
cases exercise NaN / ±Infinity.

Two crosscheck findings:

- tabs.css sidepanel variant: the base [data-component="tabs"]
  [data-slot="tabs-list"] { height: 48px } rule has (0,2,0) specificity
  and wins over the consumer's Tailwind h-11 (0,1,0). Explicit
  height: 44px in the variant block makes the 44px tab row intentional
  instead of a specificity accident.
- session.tsx: the column is now flex-1 with no explicit width, so
  transition-[width] no longer animates anything (flex-basis changes
  on flex-1 items don't go through the width transition). Strip the
  classList entirely; the aside's own transition-[width] at
  session-side-panel.tsx:315 is what actually smooths the open/close.

Round 2 crosscheck:

- clampRightPanelWidth now rejects non-number inputs (string, null)
  in addition to the non-finite guard added in round 1. Corrupted
  persisted blobs from external migration tooling could hand the
  function a string; treat like undefined → default. Two new test
  cases cover string + null.
- session-side-panel.tsx: add inline comment explaining why the 40px
  aria-hidden spacer inside Tabs.List exists (matches design prototype
  gutter) so a future editor doesn't trim it as dead space.

Two manual-test regressions:

- reviewSnap suppressed the 240ms transition on every desktopReviewOpen
  flip. That guard was there to prevent double-animation jank back when
  the session column had an explicit sessionPanelWidth() that animated
  alongside the aside. With Task 4 the session column is pure flex-1,
  so the aside is the only thing animating and the session column
  auto-adjusts per frame. reviewSnap state + requestAnimationFrame
  bookkeeping + prop are all removed.
- Right panel titlebar toggle SVG rendered at the button's 32x24 box
  because the bare <svg data-slot="icon-svg"> matched icon.css's
  [data-slot="icon-svg"] { width: 100% } without the sizing wrapper.
  Wrap in <div data-component="icon" data-size="small"> to pin it at
  16x16, matching the left sidebar toggle.

Two @smoke titles drifted after earlier PR #32 commits:
- home server picker title → "@smoke project home status panel can open the server picker dialog"
- file-tree entrypoint title → "@smoke review keeps the persistent file-tree pane for review navigation"

The curated list in e2e-smoke-tagging.test.ts still referenced the old
titles, failing the CI unit job. Sync to current titles.