Rules header bar with Add dialog

[bracyw]

Description

Implement the sub-header bar with Add, Remove, and Toggle Subscription buttons plus a search input. Add opens a dialog to create a new rule. Remove and Toggle Subscription are visible stubs — they depend on table checkbox selection from the next ticket.

Acceptance Criteria

• Header bar displays: "Rules" label, Add/Remove/Toggle Subscription buttons, search input
• Add button opens dialog with fields: topic, expr, debounce_time — submits via PUT /rules/add
• Remove and Toggle Subscription buttons disabled until rules are selected
• Search input wired to a filter signal/subject for the table to consume
• TODO: description field in Add dialog once backend supports it

Proposed Solution

Use PrimeNG Button and InputText. Add dialog via DynamicDialog (reference existing dialog patterns). Search input drives a BehaviorSubject<string>. Remove/Toggle Subscription use [disabled]="selectedRules.length === 0" — populated by table ticket. Test by creating a rule via dialog and confirming via Postman.

Mocks