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/.

Makefile

@@ -0,0 +1,12 @@
+VERSION ?= 0.0.0-dev
+
+.PHONY: package clean
+
+# Build a .deb at $(VERSION). Requires nfpm in PATH.
+# Example: make package VERSION=0.1.0
+package:
+	mkdir -p dist
+	VERSION=$(VERSION) nfpm pkg --packager deb --target dist/ -f nfpm.yaml
+
+clean:
+	rm -rf dist/