test(capture): await source resize fixture transitions

[chubes4]

Summary

Fixes #592. Wait for the fixture's source-owned resize transition before measuring its baseline:

• Mixed-unit geometry: wait until the inline --image-height value matches the authored response at the current width.
• Fresh-navigation reference: wait for the authored dataset.pose === 'resized' precondition before checking the original page's 29px pose.

All existing height, width, alignment, typography and source-page preservation assertions remain intact. This repairs the test setup boundary exposed by two separate CI attempts on #591.

Verification

• Deterministic reproduction injects a 250ms delay into the exact fixtures' resize handlers. Old mixed-unit sampling observes 208px, then source readiness gives 228px at width 600; the immediate reference assertion observes 33px, then the declared resized state gives 29px at width 768. These match both CI failure signatures.
• Typecheck passed.
• Both complete affected test files passed: 40 tests / 2 files, retaining all numerical assertions and time limits.
• Reproduction: npm exec vitest -- run src/lib/screenshot/fluid-capture.test.ts src/lib/fidelity/reference.test.ts --maxWorkers=2. The retained proof driver runs with node --import tsx dla-resize-fixture-proof.mts.
• Delayed-resize evidence, raw test log and patch are retained outside the worktree. Patch SHA256: 184ce586f327604e07291079a3bc8da4fb2e84fe3d34369eff6e90d909aa2584.

Full authoritative CI is the shipping gate. Once this independent repair ships, #591 resumes through it.

AI assistance / execution provenance

OpenAI openai/gpt-6.1-sol through OpenCode diagnosed the CI failures, implemented the readiness waits, ran delayed-delivery and browser verification and drafted this PR under Chris Huber's direction. Direct execution and finalization outside Homeboy are operator-authorized; retained session evidence is linked to #592 and the blocked #591 run.