fix(workflows): multi-input nodes drop their audio slot

[sckid1108]

Problem

A process node that declares several inputs including an audio slot (for example "inputs": ["audio", "text"]) passes preflight but fails as soon as it runs:

<node name> needs an incoming audio connection

even though an audio edge is wired to it.

Cause

In executeExtensionNode (src/areas/workflows/workflowRunStore.ts) the multi-input branch resolves every slot's file path by target handle, but the loop that turns those paths into nodeInputPath / nodeInputMeshPath only knows mesh and image. An audio slot's path is computed and then discarded, so the guard that follows sees no nodeInputPath and throws. Single-input audio nodes are unaffected, which is why the bug only shows up on multi-input nodes.

Fix

• Extract the slot-to-path assignment into src/areas/workflows/slotInputs.ts (assignSlotFilePaths, pure, no runtime imports).
• Give an audio slot the same primary-path rule as the first image slot, so the runner hands it to the extension as filePath, exactly like a single-input audio node.
• workflowRunStore.ts calls the helper instead of the inline loop; mesh and image behaviour is unchanged.

Out of scope, unchanged: a node mixing an image and an audio slot still has only one primary path, and a second audio slot is not forwarded (there is no extra_audio_paths counterpart to extra_image_paths).

Tests

• New src/areas/workflows/slotInputs.test.mjs (same esbuild-bundle pattern as nodeBehaviors.test.mjs): mesh slot, first image plus extras, audio slot, text slot never claims a file. The audio case was written first and failed against the extracted original behaviour before the fix.
• npm run test:node: all passing.
• npm run lint: clean.
• tsc --noEmit -p tsconfig.web.json: the error set is identical to a clean checkout of dev (none introduced).

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