[codex] Add workspace camera smoothness slider

[HendrikD2005]

Summary

Adds a configurable workspace camera smoothness slider for Issue #1623. The left edge (Minimal) preserves immediate pan/zoom behavior; moving the slider right increases the easing duration until the right edge (Smooth / Sanft) feels softer. The change extends the existing useWorkspace camera path and Settings appearance preferences.

Refs #1623

Scope

• In scope: browser-local 0-100 camera smoothness preference, Settings slider wiring, requestAnimationFrame interpolation, reduced-motion fallback, focused tests.
• Out of scope: new canvas/graph substrate, server persistence, BFF routes, layout/registry/connection redesign.

Reuse And No-Duplication

• Existing Keiko functionality was inspected before implementation.
• Reuses the existing useWorkspace camera owner and browser-local workspace appearance preference pattern.
• New code is limited to the documented visual-interpolation gap in Add configurable workspace camera animation mode #1623.
• Does not introduce a parallel workspace, camera, renderer, graph, or persistence subsystem.

Delivery Board

• Issue label reflects active work: status: in progress.
• Autonomous agents did not merge, enable auto-merge, close the issue, or bypass human review.
• Required project board fields and human review metadata remain maintainer/project-owner follow-up.

Note: #1623 is intentionally a standalone Feature / Task without a parent epic per maintainer instruction.

Product Impact

• UI or user workflow
• CLI or developer workflow
• Core generation engine
• Evidence, audit, or compliance artifact
• Security or supply chain
• Packaging, release, or npm publication
• Documentation or repository hygiene
• No user-facing behavior change

Verification

Local verification:

npm.cmd --workspace @oscharko-dev/keiko-ui run test -- useWorkspace.wheel.test.tsx
PASS: 1 file, 6 tests

npm.cmd --workspace @oscharko-dev/keiko-ui run test -- SettingsPanel.test.tsx
PASS: 1 file, 29 tests

npm.cmd run typecheck
PASS

npm.cmd run lint
PASS

Additional suite notes from the earlier full-suite check still apply:

npm.cmd test
FAIL: repository-wide suite is currently red on this Windows environment in unrelated filesystem/symlink/POSIX-mode and unrelated package tests.

npm.cmd --workspace @oscharko-dev/keiko-ui run test
FAIL: 222/223 files passed; failures are isolated to existing src/app/globals.css.test.ts CSS string/snapshot expectations, not touched workspace/settings files.

Reuse / gap rationale:

ADR-0026 keeps useWorkspace as the canonical workspace editor and View { zoom, x, y } as the camera record. This PR extends that hook instead of creating a parallel camera owner or canvas renderer. The gap is visual interpolation: existing wheel handling coalesced view updates with rAF but still committed the visible view directly.

Review And Closure

• The PR implements only the linked issue scope.
• Required GitHub checks pass before merge.
• Actionable review findings are fixed or explicitly dispositioned.
• Checks are repeated after the latest pushed fix.

Risk Notes

• Higher smoothness changes visible camera timing, not canonical target coordinates or zoom clamps.
• Reduced-motion users receive immediate updates at every slider value.
• Preference is browser-local and does not migrate or modify server-owned workspace state.
• Existing legacy keiko.workspace.camera.animationMode = smooth values are read as slider value 100.