Normalize object-shaped manifest inputs in the workflow preflight check

[OmarB97]

Symptom

Workflow preflight rejects a run with "Image to Image needs an incoming text connection" on a node that only takes images and has a valid image edge connected. Reported in #241 (item 1).

Root cause

WorkflowExtension.inputs is documented as an array of plain type strings ('image' | 'text' | 'mesh' | 'audio'), and validateWorkflowPreflight matches declared input types against connected edges by strict equality (outputTypes.get(edge.source) === requiredType). Some extension manifests declare inputs as an array of objects instead (e.g. modly-Codex-image-extension's image-to-image node: { name, label, type, required } per slot). A string never equals such an object, so every declared input on that node is judged missing regardless of what's actually connected. formatType's fallback branch then renders the (object-typed) missing type as "text" unconditionally, which is what actually produces the misleading "needs an incoming text connection" message.

Fix

• Normalize inputs once, in buildAllWorkflowExtensions (mockExtensions.ts) — the single place raw, untyped manifest JSON becomes a typed WorkflowExtension — mapping object entries to their .type field so everything downstream can trust the documented plain-string shape.
• Make formatType (preflight.ts) fall back to String(type) instead of silently defaulting to "text", so a future malformed/unrecognized type fails loudly instead of mislabeling.

This addresses item 1 of #241 only. Items 2 (installer requirements build order) and 3 (Codex extension's own SDK bootstrap) in that report are separate, unrelated issues and are untouched here.

Verification

• Added mockExtensions.test.mjs: reproduces the real image-to-image manifest shape (four named image slots as objects) and asserts buildAllWorkflowExtensions normalizes it to ['image','image','image','image']; also covers an already-plain-string inputs array (unchanged) and a node with no multi-input array (inputs stays undefined). Confirmed the first case fails against the pre-fix code and passes after.
• Existing preflight.test.mjs: 6/6 still passing.
• tsc --noEmit across the whole project: 0 errors.