refactor(data): restructure content directory for galaxy scale

Replace flat content/districts/ with hierarchical campaign/system/
station/district structure. Path mirrors canonical IDs, enables
glob-based discovery, and is multi-campaign/DLC ready.

- git mv 46 files preserving history
- New metadata: campaign.yaml, system.yaml, station.yaml
- Rewrite content.yaml with glob-based district discovery
- Add campaign, system, station JSON schemas
- Update district schema: hierarchy fields derived from path
- Update npc-profile schema: accept district-scoped IDs
- Add TODO to 17 dialogue/monologue pool files for generator revision
- Update _meta/README.md with new hierarchy documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

content/_meta/README.md

@@ -4,3 +4,47 @@ Directories prefixed with `_` are infrastructure, not game content. The server c
 
 - `_meta/` — Infrastructure metadata (this directory)
 - `_schema/` — JSON Schema validation files (draft 2020-12)
+
+## Directory Hierarchy
+
+Content is organized hierarchically to match the game universe:
+
+```
+content/
+  content.yaml              # Manifest: campaign list, glob discovery patterns
+  global/                   # Cross-campaign shared content (factions, enums, knowledge)
+  campaigns/
+    {campaign}/             # e.g., "main"
+      campaign.yaml
+      systems/
+        {system}/           # e.g., "krenn"
+          system.yaml
+          stations/
+            {station}/      # e.g., "sova"
+              station.yaml
+              districts/
+                {district}/ # e.g., "transit"
+                  district.yaml
+                  npcs/
+                  locations/
+                  triangles/
+                  dialogue/
+                  monologue/
+                  routines/
+                  templates/
+```
+
+## Canonical ID Derivation
+
+Identity is derived from directory path at load time — no redundant ID fields in YAML.
+
+- **District:** `{system}.{station}.{district}` (e.g., `krenn.sova.transit`)
+- **NPC (within district):** `npc:{slug}` (e.g., `npc:kael-davan`)
+- **NPC (cross-district):** `npc:{district}.{slug}` (e.g., `npc:transit.kael-davan`)
+- **Location:** `{system}.{station}.{district}.location.{slug}`
+
+## Content Discovery
+
+The loader reads `content.yaml` for enabled campaigns and their glob patterns.
+District discovery uses `systems/**/districts/*/district.yaml` — no per-district
+manifest entry needed. Adding a district = creating a directory with district.yaml.