docs: add a "how to use sensorwatch" agent skill (#16)

* docs: add a "how to use sensorwatch" agent skill

Add skills/sensorwatch/, a portable Agent Skills bundle that teaches an AI
agent to use sensorwatch against the surfaces that exist today: read the
current hardware state via the sensorwatch.native API, run the CLI logger to
collect JSON Lines history, and analyze the logs. Bundles a one-shot
scripts/snapshot.py (live snapshot -> JSON) and agents/openai.yaml for Codex
discovery.

The skill ships in the repo and sdist but not the wheel (packages already
excludes it, like examples/), so no pyproject/MANIFEST change is needed.
Agent guidance is kept read-only per SECURITY.md section 4.

Wire discoverability: turn the README roadmap line into a delivered Skills
pointer (+ a Skills section) and add a short CONTRIBUTING note.

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

* docs: document building and linking the C core (static lib + DLL)

Agents (and C/C++ consumers) had no guidance on how to build or link the native
core. Both a static library (sensorwatch_static) and a shared library/DLL
(sensorwatch) build from CMakeLists.txt, both ON by default.

README "Building the native core": add the SW_BUILD_SHARED / SW_BUILD_STATIC
toggles, single-target build recipes (tests off -> no cmocka network fetch), the
artifact locations, and a "Linking against the core" subsection -- compile static
consumers with -DSW_STATIC; the DLL resolves to dllimport on Windows; CMake
add_subdirectory/FetchContent propagates the right defines. Note that
cmake --install / find_package(sensorwatch) is still a planned follow-up.

SKILL.md: add a compact build-and-link recipe under "Other language surfaces"
with a pointer to the README section.

Verified both recipes via the VS2026 Dev Shell (Ninja): the static-only build
produces sensorwatch_static.lib and the DLL-only build produces sensorwatch.dll
plus its import library.

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

* docs: address round-1 review on the sensorwatch skill

- SKILL.md: show the real SensorwatchError text ("[-4] Sensor source is not
  running or not enabled") instead of the symbolic SW_ERR_* name, which never
  appears in str(exc); clarify the catch-all reading type is upper-case
  (OTHER/UNKNOWN) via the native API but title-case ("Other"/"unknown(<N>)")
  in the logger JSONL and read_sensors().
- snapshot.py: close the Snapshot via a context manager instead of relying on
  GC timing; emit the logger's title-case "type" labels (shared SENSOR_TYPES)
  so a snapshot matches a logged record; reject negative --indent; add type
  hints.
- CONTRIBUTING.md: correct the distribution claim -- the skill lives in the git
  repo only (its links assume the full tree), not the sdist or wheel.

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

* docs: round-2 review polish on the sensorwatch skill

- snapshot.py: the native UNKNOWN sentinel (255) now maps to a bare "unknown"
  instead of "Unknown". The native binding has already collapsed the raw HWiNFO
  code, so it cannot reproduce the logger's "unknown(<N>)" form -- the docstring
  now says so precisely rather than overclaiming a full vocabulary match.
- SKILL.md: the Recipe 1 headline example now uses the Snapshot context manager
  (with session.snapshot() as snapshot:), matching snapshot.py and the Snapshot
  docstring's recommendation.

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

* docs: address Copilot round-3 notes on snapshot.py

- Validate --type against the known ReadingType names up front: a typo now
  fails loudly (exit 2, listing the valid values) instead of silently filtering
  to an empty array that looks like "no such sensors".
- Document exit code 2 (argparse usage errors) in the script docstring and the
  SKILL.md helper notes.

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

---------

Co-authored-by: Leonard Janke <lcjanke2020@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>