feat: management UI at /manage for ingestion and sync

[turban]

Background

The Swagger UI at /docs covers all ingestion and sync operations, but it is designed for developers exploring an API — not for country health teams or HISP groups setting up a Climate API instance for the first time. The gap is discoverability and guided workflow, not missing functionality.

Goal

A simple management interface that lets operators ingest and sync data without needing to know API endpoint details or dataset template IDs.

Incremental implementation path

Step 1 — Show available dataset templates on the landing page

Extend the existing landing page (GET /) to list dataset templates from the YAML registry alongside the already-ingested datasets table. Each template row shows its name, variable, period type, and a link to the relevant Swagger endpoint or the management form (step 2).

This is zero JavaScript — server-rendered in the existing Jinja2 template. It immediately answers "what data can I ingest?" without leaving the landing page.

Step 2 — Server-rendered management forms at /manage

A new HTML page at GET /manage with simple server-rendered forms for the two most common operations:

Ingest a dataset

• Dropdown of available dataset templates (from the YAML registry)
• Start date / end date fields (pre-populated with sensible defaults)
• Extent pre-filled from the configured CLIMATE_API_CONFIG extent
• Submit → POST /ingestions

Sync

• Per-dataset sync buttons for ingested datasets
• Submit → POST /sync

Status

• Current ingestion list with dataset name, temporal coverage, publication status, and last updated time — same data as the landing page datasets table but with action buttons alongside

Server-rendered HTML forms keep the implementation consistent with the landing page pattern (Jinja2 template, importlib.resources, no JS framework). Operations are synchronous — the form submits and the page reloads with the updated status. This is sufficient for guided first-time setup and manual re-sync.

Step 3 — Richer JS-based interface (future)

Live status updates, background job progress, and log streaming would require a JavaScript frontend. This is a separate effort and only makes sense once the user base and operational requirements are better understood.

Notes

• GET /manage follows the same ?f=json content negotiation pattern as GET / — JSON clients can still access the underlying data.
• The management page should be linked from the landing page Explore section.
• No new dependencies are required — Jinja2 and Starlette form handling are already available.
• Authentication/authorisation is out of scope; Climate API instances are assumed to be deployed behind appropriate network controls.