v0.0.8: Complete GNU Taler payment lifecycle & Refactor Gateways UI

[roncodes]

Summary

This PR completes the GNU Taler payment gateway lifecycle for Ledger. It turns the existing Taler purchase, webhook, and refund primitives into a tenant-safe gateway integration with admin diagnostics, productized webhook provisioning, settlement verification metadata, wallet-aware refunds, UI visibility, and opt-in sandbox E2E support.

What Changed

• Added tenant-safe Taler webhook routing that resolves the exact company-scoped gateway from company_uuid and gateway identifiers instead of falling back to the first active gateway.
• Added internal gateway actions for testing credentials, creating a test order, registering/updating Taler webhooks, and reading diagnostics.
• Added Taler driver support for admin diagnostics, webhook provisioning, hosted Fleetbase sandbox defaults, order status checks, richer refund metadata, and refund URI propagation.
• Added gateway transaction lifecycle fields for reconciliation, refund status, wallet refund state, settlement metadata, and raw Taler details.
• Added settlement verification and sandbox E2E console commands.
• Fixed refund reversal handling so processed refunds resolve invoice context, create Ledger reversal entries, and preserve partial/full refund state.
• Updated Ledger admin UI surfaces for Taler gateway actions, diagnostics, gateway transaction details, invoice status, and refund/payment visibility.
• Updated local Docker Taler webhook payload setup to include tenant and gateway routing metadata.
• Added focused tests for Taler driver behavior, webhook routing, gateway lifecycle routes, diagnostics, settlement commands, and refund URI handling.

Hosted Sandbox Defaults

Sandbox-mode Taler gateways now default to Fleetbase's hosted Taler Merchant Backend when backend_url is blank:

• Merchant Backend: https://merchant.taler.fleetbase.io

Live gateways still require an explicit production Merchant Backend URL, and API tokens are never defaulted.

Documentation

Package-local docs/taler markdown was removed. Official GNU Taler gateway documentation now lives in the Fleetbase docs site and is tracked in fleetbase.io PR #84:

fleetbase/fleetbase.io#84

Validation

• php -l passed for all touched PHP files.
• git diff --check passed.
• Focused ESLint passed for touched JavaScript files.
• Focused Ember template lint exited successfully for touched templates, but still printed the existing invalid no-down-event-binding rule configuration.
• Focused Pest slice could not run because no Pest binary is available in this checkout.

Notes

• Live GNU Taler credentials, Merchant Backend tokens, wallet secrets, and sandbox private credentials are not committed.
• The live sandbox E2E command is opt-in and skipped unless TALER_E2E_ENABLED=true.