feat: append-only version history + bliss CLI ergonomics

Snapshot the code-bearing fields of routes (verb/path/handler), templates
(name/content/test_object), and db libraries (name/library) on every
content-changing save, so nothing edited is ever lost. Recorded in a new
`versions` table via recordVersion() hooked into the create/update functions
in db.js (the single write choke point), deduped against the latest snapshot
so no-op saves, error-flag-only route writes, and server-restart WS
re-bootstraps don't pile up. The live row stays current; old snapshots are the
undo trail. Read-only, no revert UI yet.

- migrations/004_add_versions.sql: versions table + indexes
- db.js: recordVersion/getVersions/getVersion + create/update hooks
- plumbing.js: /versions/:id and per-entity .../versions list endpoints
- bliss: `versions <type> <sid> <id>` and `version <id>` reads;
  `update-settings` (edit route_prefix/head_injection, preserving the
  untouched field); `use <url>` sticky target persisted to ~/.bliss/target
  so BLISS_URL needn't be re-exported each call
- client.js: target-file precedence (BLISS_URL > ~/.bliss/target > localhost)
- SKILL.md: document the above

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bliss-cli/SKILL.md

@@ -23,6 +23,15 @@ It logs in once and caches the session cookie under `~/.bliss/`, re-logging-in
 automatically when it expires. Run it as `node bliss-cli/bliss <command>` (or
 `./bliss-cli/bliss` if on PATH).
 
+Instead of re-exporting `BLISS_URL` every time, set a **sticky target** once —
+it persists to `~/.bliss/target` and is used until you change it (a `BLISS_URL`
+env var still overrides it when set):
+
+```bash
+bliss use https://your-instance.example.com   # set the target instance
+bliss use                                      # print the current target
+```
+
 ## The model (what you're editing)
 
 A **Structure** is a mini web app. It has **routes** (a VERB + path + a JS
@@ -42,14 +51,34 @@ bliss template <sid> <tid>             # one template incl. content + test_objec
 bliss db <sid> <dbid>                  # one db incl. its library source
 bliss files <sid>                      # files attached to a structure
 bliss logs <sid> <rid> [--since <id>]  # route logs (console.log output + errors)
+
+bliss versions <route|template|db> <sid> <id>   # save history (newest first)
+bliss version <versionId>                        # one version incl. full snapshot
 ```
 
 All emit JSON, so: `bliss structure 3 | jq '.routes[].path'`.
 
+## Version history (undo trail)
+
+Every content-changing save of a route handler, template, or db library records
+an append-only snapshot. The live row is always the current version; old ones
+are kept so nothing edited is ever lost. `versions` lists the summaries (id,
+`created_at`, `bytes`) newest-first; `version <id>` returns the full snapshot
+(the versioned fields). No-op re-saves are deduped, so identical content doesn't
+pile up. There's no revert command yet — to roll back, fetch an old snapshot and
+re-`update-*` its content:
+
+```bash
+bliss versions route 3 12                        # what saves exist
+bliss version 24 | jq -r .snapshot.handler > /tmp/old.js
+bliss update-route 3 12 --handler-file /tmp/old.js   # restore it as a new save
+```
+
 ## Writes
 
 ```bash
 bliss create-structure "<name>"                 # -> {location, id}
+bliss update-settings <sid> [--route-prefix <p>] [--head-injection <s>|--head-injection-file <f>]
 bliss clone <sid> --name "<n>" --prefix /p [--clone-dbs]
 
 bliss create-route <sid> <VERB> <path>          # VERB: GET|POST|PUT|DELETE|WS ; -> {id}