Session 0018.0 (Wave 9): rewrite legacy session refs in transcript bodies + README scoping

- Rewrite every legacy `Session L` / `Session M.1` etc. reference inside
  transcript bodies to the numeric form (`Session 0012.0` / `Session 0013.1`),
  via a mechanical Python sed pass scoped to canonical-filename transcripts
  only (502 replacements across 39 files; 21 files in this published repo +
  18 sibling files in `~/git/ohm-infra/`). The §23 rename was originally
  filename-only — session 0018.0 reverses that and rewrites the bodies too,
  so cross-references inside a transcript match the filename you'd browse
  to. The mapping table (`A → 0001` … `N → 0014`) lives in
  `SESSION-PROTOCOL.md` §1 (also amended this session) for anyone hitting
  an old external link.

- Amend README.md:
  - New "Where the record begins" section noting OHM started with two
    vibe-coded prototypes (no transcripts; the discipline that produced this
    record didn't exist yet). The transcripts here begin at the
    spec-driven-development phase — not at the literal beginning of OHM.
  - Update the existing "Sessions 0001 through 0013 originally shipped
    under a letter-form naming" paragraph to reflect that body refs are
    now also in numeric form.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -12,6 +12,29 @@ There is no GitHub mirror. The same content is rendered on-site at
 [`ohm.wiggleverse.org/docs/sessions`](https://ohm.wiggleverse.org/docs/sessions)
 (live from rfc-app v0.19.0+).
 
+<!-- operator: rewrite this section in your voice -->
+## Where the record begins
+
+OHM started with two vibe-coded prototypes — exploratory passes the
+operator built to figure out what the project wanted to be. Neither
+prototype produced a session transcript; the discipline that produced
+this record didn't exist yet, and the work was more "what does this
+even feel like to use" than "ship a deployable version."
+
+The first draft of the framework spec
+([`rfc-app/SPEC.md`](https://git.wiggleverse.org/ben.stull/rfc-app/src/branch/main/SPEC.md))
+was written off what those prototypes had taught the operator. From
+that draft onward, the build switched to spec-driven development:
+every session reads the spec, advances one feature, lands on OHM, and
+records what happened. The transcripts here start at that point — not
+at the very beginning of OHM's existence, but at the beginning of
+OHM-as-spec-driven-work.
+
+The two vibe-coded prototypes are not represented here. If you're
+trying to understand how OHM thinks, the spec is the primary text;
+the transcripts are the day-to-day record of how the spec gets
+extended in use.
+
 <!-- operator: rewrite this section in your voice -->
 ## How OHM gets built
 
@@ -108,11 +131,14 @@ Sessions 0001 through 0013 originally shipped under a letter-form
 naming (`SESSION-A` through `SESSION-M`). Roadmap item #23 (executed
 in session 0014.0) renamed every file to the zero-padded numeric
 form via `git mv` so the audit trail shows file-was-renamed rather
-than file-was-deleted-and-recreated. Transcript bodies still read
-"Session I" / "Session M.1" / etc. internally; that's deliberate —
-the rename is filename-level only, not a rewrite. The mapping table
-is in `SESSION-PROTOCOL.md` §1 (legacy form table) on the
-private-but-referenced `ohm-infra` working repo.
+than file-was-deleted-and-recreated. Initially the file-level rename
+was filename-only — the bodies still read "Session I" / "Session M.1"
+internally — but session 0018.0 also rewrote the bodies to use the
+numeric form throughout, so cross-references inside a transcript
+match the filename you'd browse to. The legacy mapping table
+(`A → 0001`, …, `N → 0014`) lives in `SESSION-PROTOCOL.md` §1 on
+the private-but-referenced `ohm-infra` working repo, in case you
+encounter a stray legacy reference in older external links.
 
 ## How transcripts get added