* fix(phase-11/09): calculator got the operator token, not the expression
The per-token scan ran before whole-expression extraction, so for a spaced
expression the first token merely containing an operator won - the bare '+'.
The whole-expression branch below it was unreachable, so the demo query from
docs/en.md returned a syntax error instead of a result.
Extract the expression first, keep the token scan as the fallback. The TypeScript
port already does whole-match extraction (code/main.ts).
'Calculate (100 + 250) * 0.15' -> 52.5 (was: unexpected EOF while parsing)
'What is 2+2' -> 4.0
'how much is 7 * 6' -> 42.0
'calculate 10/4' -> 2.5
'compute the total' -> 0.0 (unchanged fallback)
* fix(phase-11/09): extract a contiguous expression and validate it
Review feedback: filtering allowed characters out of the whole message
concatenated unrelated numbers - 'calculate 10/4 with precision 2' produced
'10/4 2', which contains '/' so it was returned and then failed to parse.
Match contiguous arithmetic runs instead, and validate each candidate through
calculator() before returning it, so a malformed run falls through to the token
scan rather than being handed to the tool.
'calculate 10/4 with precision 2' -> '10/4' -> 2.5
'Calculate (100 + 250) * 0.15' -> '(100 + 250) * 0.15' -> 52.5
'What is 2+2' -> '2+2' -> 4.0
'how much is 7 * 6' -> '7 * 6' -> 42.0
'compute the total' -> '0' -> 0.0
'what is 5 apples plus 3 oranges' -> '0' -> 0.0
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Co-authored-by: thejesh23 <thejesh23@users.noreply.github.com>
Thejesh