feat(pathfinding): first-boot prompt to pre-bake the .swb map cache (#2475)

## What

On **first boot** (right after map selection), offer to pre-bake the pathfinding `.swb` cache for the selected maps. This removes first-pathfind-after-boot latency and is now cheap — ~18 MB/facet after the v8 format work (the old ~565 MB is gone). The answer persists in `modernuo.json` as **`pathfinding.prebakeMaps`** (default **false**): asked exactly once, and skipped on headless/CI boots (redirected input) where operators can set the flag directly.

## How — a generic startup phase, not pathfinding hardcoded in the engine

The clean-console (pre-Serilog) prompt window is inside the engine startup, but UOContent isn't loaded until after `ServerConfiguration.Load`. So rather than coupling the engine to pathfinding, this adds a generic lifecycle phase:

- **`Main.cs`**: new `AssemblyHandler.Invoke("ConfigurePrompts")` — runs **after** `LoadAssemblies` (so content can participate) but **before** the first `logger.Information` (so console prompts aren't interleaved with the async console sink). The first log line moves below it. Any class can hook in with `public static void ConfigurePrompts()` and self-gate on first-boot state. No `ServerConfiguration` or pathfinding coupling added to the engine.
- **`PathCacheCommands.ConfigurePrompts()`**: the first-boot prompt (interactive-only, flag-absent-only); persists the answer.
- **`PathCacheCommands.Initialize()`** (`Invoke("Initialize")` phase, after the tile matrix loads — which the bake walks): when the flag is set, bakes any map whose `.swb` is **missing or stale** (tile-data fingerprint mismatch, via `StepCache.ComputeLiveFingerprint` / `TryReadFingerprintFromFile`). A fresh cache is a no-op, so only the first boot — or a post-client-update boot — pays the several-minute cost.

## Docs

Fixed the now-stale "~565 MB / ~1.5–2 GB / do not bake by default" section in `dev-docs/pathfinding.md` (it's 17.9 MB for Trammel, tens of MB for all six facets after v8), added a "First-boot pre-bake prompt" section, and added the `pathfinding.prebakeMaps` lever row.

## Verified

- `dotnet build UOContent -c Release` → 0 errors (rebased on #2474).
- Pathfinding/StepCache tests: **90/90 pass**.
- Bootstrap streamlining of the startup phases is intentionally left as a follow-up.

Projects/Server/Main.cs

@@ -413,8 +413,6 @@ public static class Core
 
         ServerConfiguration.Load();
 
-        logger.Information("Running on {Framework}", RuntimeInformation.FrameworkDescription);
-
         var assemblyPath = Path.Join(BaseDirectory, AssembliesConfiguration);
 
         // Load UOContent.dll
@@ -431,6 +429,14 @@ public static class Core
 
         AssemblyHandler.LoadAssemblies(assemblyFiles);
 
+        // First-boot interactive setup. Runs after assemblies are loaded (so content can
+        // register prompts) but before any Serilog output, so console prompts are not
+        // interleaved with the async console sink. Handlers self-gate on first-boot state
+        // (e.g. "is my setting already present?").
+        AssemblyHandler.Invoke("ConfigurePrompts");
+
+        logger.Information("Running on {Framework}", RuntimeInformation.FrameworkDescription);
+
         VerifySerialization();
 
         _now = DateTime.UtcNow;