Feature Request: Full Incident Management for Status Pages

Current status pages in Checkmate are limited to automatically showing `Degraded performance` when a monitor detects an issue.
Internal incidents exist, but they cannot be synced properly to the public status page (#3006), they lack detail, and they can be resolved silently without updates.

Compared to tools like **Better Stack Status** (), **Atlassian Statuspage** (), and **Instatus** (), Checkmate’s incident communication is still very basic. I personally find Better Stack’s layout and incident timeline the most intuitive.

## What I Personally Need

### 1. Manual Incidents
Support for creating manual incidents with:
`title`, `summary`, `description (markdown)`, `severity/impact`, `affected monitors`, `visibility (public/internal)`.

### 2. Updating Incidents
Ability to post update entries with states such as:
`investigating`, `identified`, `monitoring`, `resolved`, `custom`.

Updates should appear as a **chronological timeline** on the public status page.

### 3. Incident History / Timeline View
A proper history on the status page:
- day‑grouped incident history (similar to Better Stack)
- incidents shown individually when multiple are active
- expandable entries showing all timeline updates

### 4. Public Status Page Improvements
- replace the single generic message with real incidents + labels
- support multiple active incidents
- clear status summary based on severity labels

### 5. Interaction With Monitors
- option for monitors to auto‑create an incident
- auto‑resolve only if the incident has no manual updates (configurable)

## Example Use Cases
- A degradation that monitors do not detect → I want to manually create an incident and post updates.
- A failing monitor should create a proper public incident with a severity label.