feat: add deep-link support to dashboard widgets via query param

[wagmiiii]

Closes #386

Summary

Added deep-link support to the Dashboard widgets so that support agents and frontend engineers can share isolated exact views of specific components.

What changed

• Dashboard.tsx: Added useSearchParams to read the ?widget= URL parameter. When present, the page will only render the <ActionCard> that matches the query param (e.g., trust-score, active-bonds, recent-activity, shortcuts), hiding the rest. If omitted, all widgets render as normal.
• Dashboard.test.tsx: Seeded the MemoryRouter mock to accept initialEntries and added a regression test verifying that passing ?widget=active-bonds correctly filters out all other widgets.
• README.md: Documented the new deep-link query parameter under the routing index.

(Note regarding layout: When isolating a widget via the query param, it inherits the full width of its dashboard__grid container. This is a standard CSS Grid behavior and is generally acceptable for isolated debugging/support views without requiring a heavier layout refactor).

Acceptance Criteria Checklist

• The change matches the summary above.
• No regression in the existing test suite (added test to lock in new behavior).
• The change is documented where it is observable (README).
• Lint, type-check, and tests all pass locally.
• PR description references this issue with Closes #.

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