feat: initial scaffold and profiles for Schneider iEM2135, LUG heat meter v4

Seed the repo described in pda-fieldbus ADR-0009: a sibling repo that
ships device profiles independently of the fieldbus binary.

Layout:
- profiles/schneider-iem2135.json    — distilled from the inline extract
                                       rules in examples/poll-d27-g110.yaml
- profiles/lug-heat-meter-v4.json    — heat-meter profile with derived
                                       delta_temperature

Both validate against pda-fieldbus's profile.LoadDirs.

Packaging:
- nfpm.yaml builds pda-fieldbus-profiles.deb installing profiles/ to
  /usr/share/pda-fieldbus/profiles/, where the loader's DirPackaged dir
  picks them up. Recommends pda-fieldbus.
- .gitea/workflows/auto-tag.yml: same conventional-commit auto-tagging
  as pda-fieldbus, on tag push installs nfpm, builds .deb, uploads to
  repo.pda.cz/PDAT/main using the existing PDA_REPO_TOKEN secret.
- .gitea/workflows/ci.yml: JSON syntax check + schema validation by
  importing pda-fieldbus's loader and calling LoadDirs against profiles/.

profiles/schneider-iem2135.json

@@ -0,0 +1,35 @@
+{
+  "schema": "pda-fieldbus.profile/v1",
+  "device": {
+    "manufacturer": "Schneider Electric",
+    "model": "iEM2135",
+    "protocol": "mbus"
+  },
+  "meta": {
+    "version": "1",
+    "references": [
+      "Schneider iEM2000 series user manual"
+    ]
+  },
+  "points": {
+    "current": {
+      "addr": "mbus/dif:05/vif:FD/vife:DC,FF,00",
+      "unit": "ampere",
+      "dimensions": "current",
+      "description": "Total current"
+    },
+    "power": {
+      "addr": "mbus/dif:05/vif:2E",
+      "unit": "watt",
+      "dimensions": "power",
+      "description": "Active power"
+    },
+    "energy": {
+      "addr": "mbus/dif:07/vif:03",
+      "unit": "kilowatt_hour",
+      "scale": 0.001,
+      "dimensions": "energy",
+      "description": "Total active energy import"
+    }
+  }
+}