Fix caption wrapping and configurable vertical offset

[chubes4]

Summary

Fixes #2560. Captions now wrap within their pill, and recipes can configure a validated pixel offset to move them away from sticky headers or other content.

What changed

• Runtime change in `packages/runtime-playground/src/browser-annotations.ts`: captions use normal whitespace and `overflow-wrap: anywhere`; labels retain `nowrap`. Caption `offset` adds pixels to the existing vertical inset for top, center, and bottom placements.
• Runtime contract change in `packages/runtime-core/src/browser-interaction.ts`: caption offsets must be finite, non-negative numbers; offsets on other annotation shapes are rejected.
• Regression coverage in `tests/browser-annotations.browser.test.ts` verifies validation and measures wrapped text lines against the pill and viewport at a narrow viewport, including the applied offset.
• Committed as `c4762426` (`fix(annotate): wrap captions and support vertical offset`). No changelog or version strings were changed.

How to test

1. Run npm ci && npm run build && npm run test:browser-annotations; expect passes as recorded by Cook's deterministic gate.

Compatibility

Additive for captions: omitting `offset` preserves the existing placement, while caption text now wraps instead of overflowing. Labels are unaffected. Invalid or non-caption offsets are rejected during step validation.

Evidence

• Verified command npm ci && npm run build && npm run test:browser-annotations: status=succeeded; candidate commit 16e9e9c3b8b71d159ecd3adf51688456daa43cdc, tree 27da5c1a76ae95757e5bbefea8118e5ddad5d115, fingerprint 8f48f250f36cf8e746ee8dc7178d03356aa13cfdc5619781419d4f833c5025db; durable gate gate-1
• Base unchanged since verification: main remains at 0faffbf.
• CI expected: Homeboy CI after push
• Candidate adoption provenance: the candidate was promoted from the recorded Cook task execution.
• Cook deterministic verification: 1 gate(s) completed green.
• Durable run execution: Succeeded
• Reviewer-resolvable evidence from source_refs[0]: annotate caption: long text overflows the pill (white-space: nowrap) and the vertical offset is fixed #2560
• Task objective: Goal: annotate captions wrap inside their pill and accept a configurable vertical offset. Start in packages/runtime-playground/src/browser-annotations.ts (~L116-119 caption styles) and the step validation in packages/runtime-core/src/browser-interaction.ts (~L385-391); tests in tests/browser-annotations.browser.test.ts.
• Verified candidate scope: 3 changed file(s): packages/runtime-core/src/browser-interaction.ts, packages/runtime-playground/src/browser-annotations.ts, tests/browser-annotations.browser.test.ts.
• Verified finalization base: main at 0faffbf
• deterministic gate passed: sh -lc npm ci && npm run build && npm run test:browser-annotations (Passed)

AI assistance

• AI assistance: Yes
• Tool(s): Homeboy (opencode)
• Model: openai/gpt-6-luna
• Used for: Read issue annotate caption: long text overflows the pill (white-space: nowrap) and the vertical offset is fixed #2560 first, checked the existing annotation executor and shared validation contract, then added a browser regression and validated offset behavior. The focused suite passed via `node --import tsx --test tests/browser-annotations.browser.test.ts` (4 tests). The package-script launcher could not start because `tsx` IPC listener setup returned EINVAL in this environment; the direct Node test invocation worked. These are bounded observations, not controller-owned final gate results. No PR was opened or pushed because publication is controller-owned for this attempt. Runtime evidence boundary: changes are limited to the caption annotation contract, rendering, and browser tests; existing label, arrow, and other annotation behavior was not intentionally changed. AI-assisted: authored by a Homeboy cook for Extra Chill Bot.