Scaffold the Go app: auth, migrations, bundle import

Bring up the stage 1 skeleton described in the PRD, enough that the app
builds, serves, and can be populated with dishes.

- net/http server with shared-password Basic auth, /healthz outside it,
  graceful shutdown, and TZ-aware calendar days
- SQLite via modernc (pure Go, static binary), opened with WAL and a single
  connection
- migration runner: numbered SQL files embedded and applied once each inside
  a transaction, recorded in schema_migrations
- bundle import (PRD §7.3) as a live feature on the Ruoat tab: paste JSON or
  upload a file, get a per-row Finnish report. The same importer is reachable
  as `foodster -import` for repopulating a scratch database
- templ views and hand-written CSS with light-dark() theming; the Datastar
  v1.0.3 client is vendored, since the Go SDK ships no browser asset and a
  CDN would break an offline LAN

Names are normalized to sentence case rather than title case: Finnish
capitalizes only the first word of a phrase, so "Keitetyt perunat" is right
and "Keitetyt Perunat" is not. PRD §6 and §7.3 are amended to match.

Testing is behind make targets rather than ad-hoc commands: `make check` runs
lint, unit tests and scripts/smoke.sh, which exercises auth, static assets
and every import path against a scratch database on a spare port.

seeds/kotiruoat.json

@@ -0,0 +1,18 @@
+{
+  "mains": [
+    {"name": "Uunilohi",         "categories": ["fish"],       "has_sides": true},
+    {"name": "Lasagnette",       "categories": ["meat"],       "has_sides": false},
+    {"name": "Jauhelihakastike", "categories": ["meat"],       "has_sides": true},
+    {"name": "Risotto",          "categories": ["vegetarian"], "has_sides": false},
+    {"name": "Pakastepizza",     "categories": ["meat"],       "has_sides": false},
+    {"name": "Kanakeitto",       "categories": ["chicken"],    "has_sides": false},
+    {"name": "Kasvissosekeitto", "categories": ["vegetarian"], "has_sides": false}
+  ],
+  "sides": [
+    {"name": "Keitetyt perunat"},
+    {"name": "Ranskalaiset"},
+    {"name": "Muussi"},
+    {"name": "Riisi"},
+    {"name": "Pasta"}
+  ]
+}

seeds/testi.json

@@ -0,0 +1,28 @@
+{
+  "mains": [
+    {"name": "Lihapullat",        "categories": ["meat"],       "has_sides": true},
+    {"name": "Jauhelihakastike",  "categories": ["meat"],       "has_sides": true},
+    {"name": "Makaronilaatikko",  "categories": ["meat"],       "has_sides": false},
+    {"name": "Kaalilaatikko",     "categories": ["meat"],       "has_sides": false},
+    {"name": "Uunimakkara",       "categories": ["meat"],       "has_sides": true},
+    {"name": "Kanacurry",         "categories": ["chicken"],    "has_sides": true},
+    {"name": "Broilerikastike",   "categories": ["chicken"],    "has_sides": true},
+    {"name": "Kanawokki",         "categories": ["chicken"],    "has_sides": true},
+    {"name": "Lohikeitto",        "categories": ["fish"],       "has_sides": true},
+    {"name": "Uunilohi",          "categories": ["fish"],       "has_sides": true},
+    {"name": "Kalapuikot",        "categories": ["fish"],       "has_sides": true},
+    {"name": "Kasvispyörykät",    "categories": ["vegetarian"], "has_sides": true},
+    {"name": "Hernekeitto",       "categories": ["vegetarian"], "has_sides": false},
+    {"name": "Kasviscurry",       "categories": ["vegetarian"], "has_sides": true},
+    {"name": "Tortillat",         "categories": ["meat", "chicken", "fish", "vegetarian"], "has_sides": false},
+    {"name": "Kotipizza",         "categories": ["meat", "chicken", "vegetarian"],         "has_sides": false}
+  ],
+  "sides": [
+    {"name": "Perunamuusi"},
+    {"name": "Riisi"},
+    {"name": "Keitetyt perunat"},
+    {"name": "Vihersalaatti"},
+    {"name": "Höyrytetyt porkkanat"},
+    {"name": "Ruisleipä"}
+  ]
+}