Stamp the build into the output, not into a tracked file

The stamping scheme was wrong in a way worth recording. tools/stamp.js rewrote
src/build-info.js before every serve and build, so after each commit the
committed stamp named the *previous* commit — as it does right now, reading
76072ed+ while HEAD is 5c1784d — and the next serve rewrote it and dirtied the
tree again. A generated value does not belong in a tracked file if anything
routinely regenerates it.

src/build-info.js is now permanent and reads `commit: 'dev'`. tools/build.js
substitutes the real commit into the bundled output only, and fails loudly if
the substitution finds nothing to replace. So dist/theladder.html names the
commit that produced it, running from source honestly reads "0.3.0 · dev", and
the working tree never churns. tools/stamp.js is gone and `npm run serve` is a
plain static server again.

Also here, for picking this up later: a "Where things stand" section in the
README with the five open questions in the order they are likely to matter —
whether money stops mattering late, the negotiation gate that four early options
sit behind, the feedback widget nobody uses, how thin Dispatch is next to the
mailroom, and third-tier versus second-pack.

121 tests. docs/DECISIONS.md §25 corrected to describe what the code now does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VMSFHyVPitUoosW5wyEADj

package.json

@@ -6,9 +6,8 @@
   "type": "module",
   "scripts": {
     "test": "node --test \"test/**/*.test.js\"",
-    "stamp": "node tools/stamp.js",
-    "serve": "node tools/stamp.js && python3 -m http.server 8080",
-    "build": "node tools/stamp.js && node tools/build.js",
+    "serve": "python3 -m http.server 8080",
+    "build": "node tools/build.js",
     "analyze": "node tools/analyze-log.js"
   }
 }