docs: use shield branding icon

[wochinge]

Summary\n- update the GitHub Action branding icon from activity to shield\n\n## Verification\n- not run (metadata-only change)

[github-actions]

@claude review

[claude]

LGTM, trivial branding icon change.

Extended reasoning...

Overview

This PR makes a single one-line change to action.yml, updating the GitHub Action branding icon from activity to shield. Both are valid Feather icons supported by the GitHub Marketplace branding spec.

Security risks

None. This is purely cosmetic metadata used to render the action listing in the GitHub Marketplace. It has no effect on action behavior, inputs, outputs, permissions, or runtime.

Level of scrutiny

Minimal — this is a documentation/branding-only change with no logic impact. The PR title (docs: use shield branding icon) and description accurately reflect the scope.

Other factors

No bugs were flagged by the bug hunting system. The change is mechanical and self-contained, well within the criteria for automatic approval.

[github-actions]

Experiment Results: 24aa7ee

Experiment	Status	Actions
Uppercase (py)	✅ Pass	View GitHub Action Run · View in Langfuse
Uppercase (ts)	✅ Pass	View GitHub Action Run · View in Langfuse
Mixed dir (node)	✅ Pass	View GitHub Action Run · View in Langfuse
Mixed dir (python)	✅ Pass	View GitHub Action Run · View in Langfuse
Regression fixture	❌ Regression	View GitHub Action Run · View in Langfuse

Details

✅ Uppercase (py) (Source)

Score	Value
avg_accuracy	1.000

Item results (3)

Item	Input	Expected	Output	exact_match
1	langfuse	LANGFUSE	LANGFUSE	1.000
2	world	WORLD	WORLD	1.000
3	hello	HELLO	HELLO	1.000

✅ Uppercase (ts) (Source)

Score	Value
avg_accuracy	1.000

Item results (3)

Item	Input	Expected	Output	exact_match
1	langfuse	LANGFUSE	LANGFUSE	1.000
2	world	WORLD	WORLD	1.000
3	hello	HELLO	HELLO	1.000

✅ Mixed dir (node) (Source)

Score	Value
avg_accuracy	1.000

Item results (3)

Item	Input	Expected	Output	exact_match
1	langfuse	LANGFUSE	LANGFUSE	1.000
2	world	WORLD	WORLD	1.000
3	hello	HELLO	HELLO	1.000

✅ Mixed dir (python) (Source)

Score	Value
avg_accuracy	1.000

Item results (3)

Item	Input	Expected	Output	exact_match
1	langfuse	LANGFUSE	LANGFUSE	1.000
2	world	WORLD	WORLD	1.000
3	hello	HELLO	HELLO	1.000

❌ Regression fixture (Source)

RegressionError: synthetic regression triggered by e2e fixture

Item results (3)

Item	Input	Expected	Output	exact_match
1	langfuse	LANGFUSE	LANGFUSE	1.000
2	world	WORLD	WORLD	1.000
3	hello	HELLO	HELLO	1.000