feat(config): lens sections - a repository's own text appended to a shipped charter

A lens has one charter, the one this pipeline ships; what a repository
knows that is not general to the lens - its platform and layers, the
record it keeps its decisions in, what its users already have, the
calibration entries that are its own - goes in a file the config names
for the lens (lenses.<name>.section), and Charter appends it after one
blank line. The charter sha in every reuse key covers the combined text.

The config refuses a path outside the repository - absolute, or
climbing out with `..` - by the check slots.dir had, now one both
settings share; a file missing or one the run could not use (a dangling
link, unreadable, not UTF-8) is a problem too, checked through the
reader Charter uses (Prompt::ReadSection), so a section is never
dropped in silence, and a name that is no lens is the unknown key it
always was. Nothing lists a directory, so what lies beside the files is
no concern of the config's: a directory listed would have to tolerate or
refuse every foreign entry. The run logs which charters got one.

The better-solution charter gains a consumer's general entry
(2026-10-31: a mechanism reworked a second time in one submission is the
signal to derive the fix at every layer the data crosses). The procedure
names the section wherever it names the charter: among the config's keys,
in the lens inputs, in the reuse rule (an edit to either re-runs the lens)
and in the feedback loop, which routes a repository's own lesson to its
section and a general one to the shipped charter.

interfaces/Crafter.Review-Core.cppm

@@ -40,9 +40,10 @@ export namespace Crafter::Review {
     void SetHome(std::filesystem::path home);
     // Home()/process/lenses.
     std::filesystem::path LensDir();
-    // The sha256 of each lens file — the text read with universal newlines,
-    // as UTF-8 — keyed by file name. Every charter's is part of its lens's
-    // reuse keys, so --version and the run log print them: a stale home shows
-    // up there before it shows up as nothing being reused.
+    // The sha256 of each shipped lens file — the text read with universal
+    // newlines, as UTF-8 — keyed by file name. A lens's reuse keys carry its
+    // charter's (the combined text's when lenses.<name>.section gives the
+    // lens a section of the repository's own), so --version prints these: a
+    // stale home shows up there before it shows up as nothing being reused.
     std::vector<std::pair<std::string, std::string>> CharterHashes();
 }