feat: adapter contract, commerce proof-of-fit, and reusability docs

Proves the engine did not stay video-specific during extraction.

- application adapter contract in core (createApplicationAdapter,
  evaluateObject, collectTargets): an object names the targets that govern it
  and the strictest verdict reaching any of them wins, so denying a seller
  takes their whole catalogue down with no cascade logic in the application
- examples/commerce: a marketplace on the public API covering all ten
  proof-of-fit behaviors the plan requires, including that no core change was
  needed. One product, one snapshot, four surfaces, four different verdicts.
- README, integration guide, per-example README, CHANGELOG, four ADRs, and
  GPL-3.0-or-later LICENSE (the license was listed in Phase 1 but missing)
- checkpoints rewritten to reflect actual state and to say plainly which
  migration-plan phases belong to the consumer repos rather than here

Fixes a real gap found by the proof-of-fit: composeDecisions kept only the
first decision's evidence, so an object governed by several targets lost the
evidence that drove its verdict. Evidence now merges — counts summed,
contributor lists unioned, flags or-ed.

556 tests; lint, typecheck, and per-package type build clean.

package-lock.json

@@ -8,7 +8,8 @@
       "name": "nostr-governance",
       "version": "0.1.0",
       "workspaces": [
-        "packages/*"
+        "packages/*",
+        "examples/*"
       ],
       "devDependencies": {
         "@types/node": "^22.10.0",
@@ -19,6 +20,14 @@
         "node": ">=22"
       }
     },
+    "examples/commerce": {
+      "name": "@nostr-governance/example-commerce",
+      "version": "0.1.0",
+      "dependencies": {
+        "@nostr-governance/core": "*",
+        "@nostr-governance/runtime": "*"
+      }
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.21.5",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.21.5.tgz",
@@ -438,6 +447,10 @@
       "resolved": "packages/core",
       "link": true
     },
+    "node_modules/@nostr-governance/example-commerce": {
+      "resolved": "examples/commerce",
+      "link": true
+    },
     "node_modules/@nostr-governance/nostr": {
       "resolved": "packages/nostr",
       "link": true