docs: correct PM1 particulate size bound (1 μm, not 0.1 μm)

[bluetoothbot]

What: Fix the PM1 device-class comment — it documented particulate matter <= 0.1 μm, which is wrong.

Why: PM1 is particulate matter up to 1 micrometer, consistent with the rest of the family (PM4 <= 4 μm, PM10 <= 10 μm, and HA's own pm1 definition). 0.1 μm is PM0.1 — a different, finer fraction. Wrong API docs mislead integrators about what a pm1 entity actually measures.

How: One-line comment correction in sensor/device_class.py. The enum value ("pm1") was already correct, so this is documentation-only — no behavior change. Added a small regression test pinning the PM-family device-class identifiers, following the repo's existing == "value" convention (test_init.py), since those strings are the Home Assistant interop contract.

Testing: pytest tests/ — 10 passed (8 existing + 2 new).

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Quality Report

Changes: 2 files changed, 21 insertions(+), 1 deletion(-)

Code scan: clean

Tests: passed (10 passed)

Branch hygiene: clean

Generated by Kōan post-mission quality pipeline

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.37%. Comparing base (31bd826) to head (4ee8e18).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #139   +/-   ##
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  Coverage   94.37%   94.37%           
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  Files          12       12           
  Lines         480      480           
  Branches        5        5           
=======================================
  Hits          453      453           
  Misses         26       26           
  Partials        1        1           

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