Fix slow pcb doc --package @stdlib

[akhilles]

Also, left align registry component preview images.

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Note

Medium Risk
Changes dependency resolution semantics in --locked mode (no longer creates/updates pcb.sum and allows it to be absent), which can affect CI reproducibility expectations across commands. Doc generation now shares a single resolved dependency context, reducing eval overhead but potentially changing which dependencies are loaded during signature extraction.

Overview
Speeds up pcb doc generation by resolving workspace dependencies once up front and reusing the resulting ResolutionResult when evaluating each .zen file for signatures (instead of resolving per file).

Adjusts --locked behavior during dependency resolution: it now verifies pcb.sum only when present, does not create/update it when missing, and updates CLI/docs/tests accordingly (including a new test ensuring pcb build --locked succeeds without pcb.sum).

Tweaks registry TUI image previews to fit while left-aligning images (no centering offset).

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