Full common split: composite tsconfigs and target-* modules

- Add composite TypeScript projects for common/primitives and common/runtime
- Decouple primitives from runtime (buffer service interfaces, UnicodeProperties, CellTypes, etc.)
- Move Types.ts to runtime; re-export primitive types from runtime/Types
- Rename src/browser -> src/target-browser, src/headless -> src/target-headless
- Update import paths (target-browser/*, target-headless/*) across repo
- Fix esbuild outbase so common/* and target-* resolve under out-esbuild/
- Point unicode addons at primitives for UnicodeTypes/UnicodeProperties
- Update ARCHITECTURE.md and AGENTS.md

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

test/benchmark/Terminal.benchmark.ts

@@ -7,7 +7,7 @@ import { perfContext, before, ThroughputRuntimeCase } from 'xterm-benchmark';
 
 import { spawn } from 'node-pty';
 import { Utf8ToUtf32, stringFromCodePoint } from 'common/input/TextDecoder';
-import { CoreBrowserTerminal } from 'browser/CoreBrowserTerminal';
+import { CoreBrowserTerminal } from 'target-browser/CoreBrowserTerminal';
 
 perfContext('Terminal: ls -lR /usr/lib', () => {
   let content = '';

test/benchmark/tsconfig.json

@@ -5,6 +5,7 @@
       "es2021",
     ],
     "outDir": "../../out-test/benchmark",
+    "rootDir": "../..",
     "types": [
       "../../node_modules/@types/node"
     ],
@@ -18,7 +19,7 @@
         "../../src/common/runtime/*",
         "../../src/common/*"
       ],
-      "browser/*": [ "../../src/browser/*" ],
+      "target-browser/*": [ "../../src/target-browser/*" ],
       "Terminal": ["../../src/Terminal"]
     },
   },
@@ -31,6 +32,6 @@
   ],
   "references": [
     { "path": "../../src/common" },
-    { "path": "../../src/browser" },
+    { "path": "../../src/target-browser" },
   ]
 }