chore(agent): add CHANGELOG, version the agent at 0.1.0

- CHANGELOG.md with the v0.1.0 (slice 1) entry
- main: version var (0.1.0, ldflags-overridable) + --version flag; version shown
  in selftest header and startup log

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,55 @@
+# Changelog
+
+All notable changes to **felhom-agent** are recorded here. Update on every code
+change that gets pushed.
+
+## v0.1.0 — Scaffold + `proxmox` interaction layer (slice 1) (2026-06-08)
+
+First slice: stand up the host-agent project and its foundation — the typed
+Proxmox interaction layer every other module will call. No reconcile loop, hub
+client, signing, or storage/backup orchestration yet (later slices).
+
+### Added
+- **Project scaffold**: module `gitea.dooplex.hu/admin/felhom-agent`, binary
+  `felhom-agent` (`cmd/felhom-agent/`), Go 1.24, zero external dependencies
+  (pure stdlib). `--version` flag; `version` var overridable via
+  `-ldflags "-X main.version=<v>"`.
+- **`internal/proxmox` — API backend (`Client`)**: hand-rolled REST client over
+  `https://<host>:8006/api2/json` with `PVEAPIToken` auth. Typed read ops
+  (`Version`, `Nodes`, `NodeStatus`, `ListLXC`, `GuestStatus`, `GuestConfig`,
+  `ListStorage`, `NodeStorage`, `StorageContent`) and async mutating ops
+  returning a UPID (`RestoreLXC` — the primary create path, `Vzdump`, `Snapshot`,
+  `Rollback`, `DeleteSnapshot`, `SetConfig`, `Start`, `Stop`).
+- **`WaitTask`**: polls `GET /nodes/{node}/tasks/{upid}/status` until stopped, then
+  asserts `exitstatus == "OK"` (authorization can surface at task execution, not
+  the POST — phase1-2 §1.3). Exponential backoff (1s→5s cap), context
+  cancellation + timeout. `*APIError` parses the offending privilege from a 403;
+  `*TaskError` parses it from a failed task exitstatus + log tail.
+- **`internal/proxmox` — fenced root-CLI backend (`Privileged`)**: limited to the
+  three proven OS-root exceptions only — `CreateGoldenLXC` (keyctl `pct create`),
+  `MountUSBByUUID`, `SMART`, `Sensors`; each cites why it can't be the API. Fence
+  is structural (Client never shells out, Privileged never makes an HTTP call) and
+  asserted in tests.
+- **TLS trust**: SHA-256 leaf-cert pinning (the host serves a self-signed cert) or
+  a CA file; an explicitly-named `insecure_skip_verify` that is off by default. No
+  blanket verification disable.
+- **`internal/config`**: JSON config file + `FELHOM_AGENT_*` env overrides; the
+  token secret is never logged (`Redacted()`).
+- **`internal/log`**: slog setup (text, stderr, configurable level).
+- **`cmd/felhom-agent --selftest`**: read-only health report against a live host
+  (version/nodes/status/guests/storage); `--selftest=task --vmid N` exercises
+  `WaitTask` on a reversible snapshot→rollback→delete op (gated; default selftest
+  mutates nothing).
+- **Tests**: unit tests with a mock HTTP transport + mock runner (UPID parse,
+  `WaitTask` running→OK / failed-403 / timeout / ctx-cancel, 403→privilege error,
+  response decoding against shapes captured live from `demo-felhom`, config
+  redaction, and the API-vs-root routing fence).
+
+### Notes
+- Types are grounded in the spike findings
+  (`felhom.eu/documentation/proxmox-platform.md`, `tests/phase{0,1-2,3}-findings.md`)
+  and the exact JSON shapes captured live from `demo-felhom` (PVE 9.2.2).
+- Verified: `go build/vet/test` green on Go 1.24.4 (build server) and a live
+  read-only `--selftest` against the demo host with TLS fingerprint pinning.
+- The 16-privilege `FelhomAgent` role + privsep token (role on **both** user and
+  token) is provisioned out-of-band; the agent only consumes the token.