Allow path-only updates to existing compute volumes

[v01dstar]

insta compute volume web --mount-path /app/storage now stages a mount path without requiring --size. Output distinguishes pending and applied paths, explains that deployment restarts the service, and reminds users to update application configuration. Normalized unchanged paths remain a no-op.

Validation: all 84 test files passed (1,587 tests passed, 121 skipped); typecheck and build passed. Requires the companion platform API change.

Part of InsForge/instacloud#153.

Runtime dependency: https://github.com/InsForge/instacloud-compute/pull/291
Platform dependency: https://github.com/InsForge/instacloud-platform/pull/504

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Summary by cubic

Allows changing an existing compute volume's mount path without respecifying --size. Previously --mount-path required --size; now a path-only edit is staged as pending and applied on the next deploy, which restarts the service. Output distinguishes pending and applied paths and reminds you to update application configuration; unchanged paths remain a no-op.

Rollout notes

• Requires the companion platform API change (InsForge/instacloud-platform#504).
• Deploying applies the pending path and restarts the service; update application paths, variables, and startup commands yourself.
• Part of InsForge/instacloud#153.

^{Written for commit d9f3ce7. Summary will update on new commits.}