refactor: replace magic numbers with named carbon factor constants in…

[ekwe7]

closes #470

Summary

Replaces undocumented magic numbers (0.05 and 0.5) in
src/routes/investor.ts with named, exported, and documented constants
(CARBON_OFFSET_FACTOR and CARBON_CREDIT_FACTOR), following the codebase's
existing pattern established in src/lib/scoring.ts.

Context & Motivation

Previously, the carbon calculation math in investor.ts used bare float
literals directly inside .reduce() and .map() callbacks. These numbers are
key inputs in converting solar power output and green impact scores into
investor-facing metric figures (total_carbon_offsets_tonnes and
carbon_credits_issued).

By extracting these as named constants:

• The intent behind the formula is clear and self-documenting.
• Any future adjustment to carbon offset or credit factors can land in a
single place.

Changes Made

• src/routes/investor.ts:
• Exported and documented CARBON_OFFSET_FACTOR = 0.05 (used in GET
/dashboard).
• Exported and documented CARBON_CREDIT_FACTOR = 0.5 (used in GET
/compliance-report and POST /custom-report).
• Updated carbon offset and credit calculations to reference these
constants.
• src/tests/investor.test.ts:
• Imported CARBON_OFFSET_FACTOR and CARBON_CREDIT_FACTOR.
• Added unit test suite verifying constant exports.

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