Add AI Credits management dashboard with source-filtered historical credits

[Copilot]

This update implements the AI Credits management experience on top of the existing widget flow, consolidating post-purchase controls and account visibility into one coherent screen. It adds the required sections and behavior, including mandatory historical source filtering with streamCron excluded by default.

• Management dashboard surface

  • Introduces a unified post-purchase management view with:
    • bonus badge (+10% / +20%) and explanatory help toggle
    • AI credits summary (total now, estimated monthly stream) and Buy/Add credit action stub
    • G$ account overview (wallet balance + deposited G$)
    • stream management subsection (current flow, Update flow action stub)
    • operator section (operator address, sign/generate actions, consent state, public/private key display)

• Historical credits + mandatory source filter

  • Extends historical entries with source and gdAmount metadata.
  • Adds required source controls: deposit | streamUpdate | streamRequest | streamCron.
  • Default filter excludes streamCron until explicitly enabled.
  • Handles filtered-empty state with explicit UI feedback.

• Data shaping and mock backend alignment

  • Enhances backend usage-entry mapping to expose filterable credit origin fields.
  • Updates mock settlement/event generation to emit source-aware credit entries compatible with management history rendering.

• QA fixture and smoke coverage alignment

  • Adjusts widget fixture states and smoke assertions to validate management sections and source-filter behavior against the new UI contract.

<UsageLog entries={state.usageLog} />
// UsageLog now enforces source filtering with default enabled sources:
// ['deposit', 'streamUpdate', 'streamRequest']
// `streamCron` is hidden until the user enables it.