Fix incorrect age adjustment values in Charlson documentation

[Copilot]

The Age Adjustment section in docs/calculators/charlson.md was off by one — it listed +1 for ages 40–49, +2 for 50–59, etc., contradicting the original Charlson publication and the actual implementation.

The code ((age - 40) // 10 clamped to 0–4) and tests were already correct; only the docs were wrong.

Changes

• docs/calculators/charlson.md: Corrected age score table to reflect actual behaviour:

Age range	Was (wrong)	Now (correct)
40–49	+1	+0
50–59	+2	+1
60–69	+3	+2
70–79	+4 (grouped with 80+)	+3
80+	+4 (grouped with 70+)	+4