feat(lenses): the commit-truth lens, repo-facts, as Gate 4

Every claim in every commit message, and in the documentation the range
adds or changes, proven or gone. The lens's block kinds are text, doc and
slot: a message unit is keyed on its text, the base and the code up to its
commit (MessageDeps); a documentation unit on its file, its normalised
text, the base and the code of the whole range (DocKeyParts); a diffstat on
its text alone; whole:order and whole:absent are asked in slot passes of
its own, never stored. A documentation file's diff header and a part the
commit writes nothing in are a mechanical n/a. Budgets 60/40 for a text or
doc block, 50/35 for a slot; one read. Gate 4, after the proofs, so the
messages and documents are read once the code they describe has settled;
the owner's gate is 5.

The goldens that follow from the lens table are derived by
tests/Goldens/derive.py, which asserts that the recorded table still
reproduces the recorded entries before it writes.

Proven, with the opt-in commit after this one: the suite (26 passed); a dry
run of a scratch range (2 commits, a README with sections) by the previous
binary and this one with the three static lenses on and the rest off, 25
prompts and 4 system files byte for byte; with repo-facts on as well,
those files unchanged and 10 passes and 1 system file added.
The lens's firing proof in this pipeline is owed (the owner's go).

process/templates/config.json

@@ -26,6 +26,10 @@
     "repo-security": {
       "run": true,
       "environment": "none"
+    },
+    "repo-facts": {
+      "run": true,
+      "environment": "none"
     }
   },
   "supabase": {