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/.

nfpm.yaml

@@ -0,0 +1,28 @@
+# nfpm config — package profiles/ as /usr/share/pda-fieldbus/profiles/
+# Version is injected at build time:
+#   nfpm pkg --packager deb --target dist/ -f nfpm.yaml -v "$VERSION"
+
+name: pda-fieldbus-profiles
+arch: all
+platform: linux
+version: ${VERSION}
+section: contrib/utils
+priority: optional
+maintainer: p.d.a. <info@pda.cz>
+vendor: p.d.a.
+homepage: https://git.pda.cz/PDAT/pda-fieldbus-profiles
+license: MIT
+description: |
+  Device profiles for pda-fieldbus.
+  Reusable JSON descriptions of M-Bus and Modbus device models — points,
+  units, scaling, and derived values — consumed by pda-fieldbus poll
+  via `profile: <name>` references.
+
+contents:
+  - src: profiles/
+    dst: /usr/share/pda-fieldbus/profiles/
+    type: tree
+
+deb:
+  fields:
+    Recommends: pda-fieldbus