Effective config with source tracking, Dnsmasq page, and test harness

- Effective config: track value sources (ConfigValueSource, EffectiveConfigSources)
  and show readonly badges/tooltips for non-managed files. Multi-value options
  use ValueWithSource/PathWithSource for JSON. StatusClient uses camelCase
  serialization for reliable deserialization.
- Parsing: align with dnsmasq (conf-file/conf-dir order, suffix filter, case-
  sensitive keys). DnsmasqConfIncludeParser and DnsmasqConfigSetService build
  effective config and sources. New DnsmasqConfigSetServiceTests.
- UI: rename Overview/Home to Dnsmasq (page, nav, doc comments). Add
  EffectiveConfigOptionItem and EffectiveConfigMultiValueRow components.
  Dnsmasq.razor uses them; Hosts.razor shows addn-hosts with source. Encode
  server-derived strings in markup to avoid XSS.
- Home section namespace: Components.Home -> Components.Dnsmasq (LogsSection,
  StatusSection, _Imports).
- Test data: expand testdata (README, resolv.dnsmasq, hosts.extra, dnsmasq.d
  configs). dhcp.conf static IP aligned with testnet.
- agents.md: add agent instructions for test harness and conventions.

agents.md

@@ -0,0 +1,80 @@
+# Agent instructions: dnsmasq-webui
+
+## Test harness (Docker)
+
+The test harness runs the app and dnsmasq in Docker with DHCP clients so you can test the UI and effective config against real dnsmasq.
+
+**Script:** `scripts/prepare-test-mount.sh`  
+**Compose file:** `docker-compose.test.yml`
+
+### Start the harness
+
+From the repo root:
+
+```bash
+./scripts/prepare-test-mount.sh
+```
+
+This will:
+
+1. Clear `testdata-mount/` (unless you pass `--no-clear`)
+2. Sync `testdata/` → `testdata-mount/`
+3. Remove any `*dnsmasq-webui*.conf` in the mount so dnsmasq starts clean
+4. Run `docker compose -f docker-compose.test.yml up -d --build`
+
+- **Quick restart (no image rebuild):** `./scripts/prepare-test-mount.sh --no-build`
+- **Prepare mount only (no start):** `./scripts/prepare-test-mount.sh --prepare-only`  
+  Then start manually: `TESTDATA_MOUNT=./testdata-mount docker compose -f docker-compose.test.yml up -d [--build]`
+- **Preserve mount (e.g. keep leases):** `./scripts/prepare-test-mount.sh --no-clear --no-build`
+
+App is at **http://localhost:8080**. Main config path in the container is `/data/dnsmasq-test.conf`; managed file is `zz-dnsmasq-webui.conf` in the same directory.
+
+### Stop the harness
+
+```bash
+./scripts/prepare-test-mount.sh --stop
+```
+
+Runs `docker compose -f docker-compose.test.yml down` (stops and removes containers/networks). Does not change the mount directory.
+
+### Clean (stop + clear mount)
+
+```bash
+./scripts/prepare-test-mount.sh --tidy
+```
+
+Stops the harness and deletes the contents of `testdata-mount/` so the next run starts from a clean sync of `testdata/`.
+
+### Custom paths
+
+- `--source DIR` — Source to sync from (default: `testdata`)
+- `--mount DIR` — Mount directory (default: `testdata-mount`). The script exports `TESTDATA_MOUNT=./DIR` when you use `--mount`, so compose uses it.
+
+Example: sync from a custom dir and start:
+
+```bash
+./scripts/prepare-test-mount.sh --source myfixtures --mount mymount
+```
+
+### Help
+
+```bash
+./scripts/prepare-test-mount.sh -h
+```
+
+## Unit tests
+
+From the repo root:
+
+```bash
+dotnet test
+```
+
+Build only: `dotnet build`
+
+## Test data
+
+- **testdata/** — Source for the harness mount. Synced to `testdata-mount/` by `prepare-test-mount.sh`. Unit tests read from the copy in the test output dir. See **testdata/README** for the full layout.
+- **testdata/dnsmasq-test.conf** — Harness main config (`/data/dnsmasq-test.conf`). Richer config: multiple `server=`, `addn-hosts=`, `address=`, `listen-address=`, `conf-dir=/data/dnsmasq.d`.
+- **testdata/dnsmasq.d/** — Included configs (01-other.conf, 02-servers.conf, dhcp.conf). App creates `zz-dnsmasq-webui.conf` here when running.
+- **testdata/hosts**, **testdata/hosts.extra** — Addn-hosts files so effective config has multiple addn-hosts; UI can show source per path.