Reconcile docs with code across the accuracy-sweep items (closes #74)

Documentation only. Corrects the ARCHITECTURE.md chunk sizes and the fx
config type; documents the process-wide PID lock, the `ls`/`rm` aliases,
`VAULTIK_CPUPROFILE`/`VAULTIK_MEMPROFILE`, the `age_secret_key` key and
its threat-model caveat, and how zstd levels 1-19 collapse onto four
presets; narrows the output-style claim to match reality; and links
ARCHITECTURE.md and config.example.yml from the README. The two
behaviour changes the sweep surfaced are deferred to #149 (route direct
stdout through internal/ui) and #150 (scope the lock), each linked from
the text. DATAMODEL.md and REPOSTRUCTURE.md were already linked.

model: claude-opus-4-8

ARCHITECTURE.md

@@ -63,7 +63,7 @@ A content-addressed unit of data. Files are split into variable-size chunks usin
 - `ChunkHash`: SHA256 hash of chunk content (primary key)
 - `Size`: Chunk size in bytes
 
-Chunk sizes vary between `avgChunkSize/4` and `avgChunkSize*4` (typically 16KB-256KB for 64KB average).
+Chunk sizes vary between `avgChunkSize/4` and `avgChunkSize*4` (2.5MB-40MB for the 10MB default average).
 
 #### FileChunk (`database.FileChunk`)
 Maps files to their constituent chunks:
@@ -120,7 +120,7 @@ The CLI uses fx for dependency injection. Here's the instantiation order:
 ```go
 // cli/app.go: NewApp()
 fx.New(
-    fx.Supply(config.ConfigPath(opts.ConfigPath)),  // 1. Config path
+    fx.Supply(config.Path(opts.ConfigPath)),         // 1. Config path
     fx.Supply(opts.LogOptions),                      // 2. Log options
     fx.Provide(globals.New),                         // 3. Globals
     fx.Provide(log.New),                             // 4. Logger config
@@ -193,7 +193,7 @@ scanner := v.ScannerFactory(snapshot.ScannerParams{
 - **Created by**: `chunker.NewChunker(avgChunkSize)`
 - **When**: Inside `snapshot.NewScanner()`
 - **Configuration**:
-  - `avgChunkSize`: From config (typically 64KB)
+  - `avgChunkSize`: From config (default 10MB)
   - `minChunkSize`: avgChunkSize / 4
   - `maxChunkSize`: avgChunkSize * 4