feat(pipeline): MP1b - acdream-bake CLI

New offline console tool driving AcDream.Content.MeshExtractor (the SAME
extraction code the live client runs, per MP1a) to produce a versioned
pak file. Arguments: --dat-dir (required), --out (default acdream.pak
next to the dats), --ids/--landblocks (dev filters), --threads (default
Environment.ProcessorCount).

Enumeration mirrors existing idioms rather than inventing new ones:
GfxObj/Setup ids via DatCollection.GetAllIdsOfType<T>() (src/AcDream.Cli/
Program.cs); EnvCell ids by walking dats.Cell.Tree for LandBlockInfo
entries (low 16 bits == 0xFFFE) and then the firstCellId+NumCells range
per landblock (the same idiom as GameWindow.BuildPhysicsDatBundle /
BuildInteriorEntitiesForStreaming). GetAllIdsOfType<T>() does not cover
cell-dat range-based types, hence the manual walk.

BakeDatCollectionAdapter is a from-scratch copy of AcDream.App.Rendering.
Wb.DatCollectionAdapter (which is `internal` to AcDream.App and, more
importantly, referencing AcDream.App would drag Silk.NET/GL into the
bake tool — a hard violation of "no Silk.NET anywhere"). It's plain dat-
access glue, not an AC-specific algorithm, so a small duplicate is the
right call over inventing a shared-but-App-rooted package.

Particle-preload GfxObjs MeshExtractor side-stages mid-extraction
(sideStagedSink, thread-safe ConcurrentQueue per MP1a's documented
contract) are deduped against the primary GfxObj set and against each
other before being written as their own GfxObjMesh entries.

ConsoleErrorLogger is a minimal hand-rolled ILogger (stderr, Warning+)
rather than NullLogger — MeshExtractor's LogError/LogWarning calls on
malformed dat entries must stay visible per the project's "logger
injection for silent catches" lesson.

Progress line every 5s (baked/total, failures, elapsed, ETA); a
malformed dat entry is caught per-id and counted as a failure, never
fatal — matches the runtime's own per-id try/catch behavior. Failures
report is printed at the end, capped at 200 lines.

Smoke-tested against the real dats on this machine: --ids
0x01000001,0x02000001 baked 1 GfxObj (40 vertices) + 1 Setup (34 parts)
in 1.4s with 0 failures; a follow-up run adding EnvCell 0xA9B40100
(Holtburg's first interior cell) baked all three asset types
successfully. PakReader opened both scratch paks and read back
deep-correct ObjectMeshData; scratch files deleted after verification.

*.pak added to .gitignore in this commit per the plan.

.gitignore

@@ -91,3 +91,7 @@ C[€-
 # Junction to Claude Code per-project memory (Obsidian vault visibility)
 claude-memory
 studio-shots/
+
+# MP1b acdream-bake output — user-machine artifact, never committed
+# (docs/superpowers/plans/2026-07-05-mp1b-pak-and-bake.md, Task 5).
+*.pak