VACUUM snapshot metadata through the sqlite driver, not a CLI (closes #120)

snapshot create compacted the metadata database by running a sqlite3 command-line binary, after every blob had already been uploaded. On a host without that binary, which includes anyone who installed with go install, the backup failed at the last step, and two tests failed the same way.

VACUUM now runs through the Go sqlite driver the program already uses, and its error is returned to the caller. The runtime Docker image no longer installs the sqlite package, since nothing in the binary calls it.

model: claude-opus-4-8 (implementation, review); claude-fable-5-1 (merge)

TODO.md

@@ -25,6 +25,15 @@ release" is exactly the contradiction
 
 # Completed Steps
 
+- 2026-09-21: Made `snapshot create` VACUUM the per-snapshot metadata
+  database through the `modernc.org/sqlite` driver instead of shelling
+  out to the external `sqlite` command-line binary (issue #120). A
+  backup no longer needs that binary on `PATH`, so `make check` passes
+  on a stock `go install` host; `script/bootstrap` and the `Dockerfile`
+  (both the test-build and the shipped runtime stage) no longer install
+  it, and a new test asserts the uploaded database keeps no pages from
+  deleted rows. Dropped the now-false note on the 2026-08-07 entry below
+  that said bootstrap installs it.
 - 2026-09-21: Made `.gitea/workflows/check.yml` run on pushes to `main`
   and `next` and on pull requests against either, so unit PRs (whose
   base is `next`) and `next` itself get a CI run instead of relying on a
@@ -529,7 +538,7 @@ release" is exactly the contradiction
   was green was wrong.
 - 2026-08-07: Added the standard `.golangci.yml` and `.editorconfig`
   (issue #59); lint findings under the new config are tracked in issue
-  #61. `script/bootstrap` now installs sqlite3 (needed by tests).
+  #61.
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
   Makefile shims, README Entrypoints section
 - 2026-07-02: Consolidated CLI verbs, retired overlapping commands; bound