docs: add form interaction guidance

[honor2030]

Summary

• Add a forms.md interaction skill for framework-managed inputs and modal form verification.
• Document fill_input() as the default path for React/Vue/Ember-style controls where type_text() / direct DOM value changes can bypass framework state.
• Include a no-auth public Ember modal/input page that can be used for experimentation without LinkedIn credentials.

Refs #148.

Test Plan

• uv run --with pytest --with pillow python -m pytest tests/unit/test_helpers.py -q
• uv run --with pytest --with pillow python -m pytest tests -q
• uv run python -m compileall src tests
• uv pip check --python .venv/bin/python
• uv run --with ruff python -m ruff check --select B SKILL.md interaction-skills/forms.md

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Summary by cubic

Add form interaction guidance for framework-managed inputs, recommending fill_input() over type_text() and outlining how to verify modal form submissions. Updates SKILL.md to include forms.md and adds a public Ember modal page for safe testing; supports #148.

^{Written for commit 9c4a5fa. Summary will update on new commits.}

[browser-harness-review]

✅ Skill review passed

Reviewed 2 file(s) — no findings.

[cubic-dev-ai]

No issues found across 2 files