Add M-Pesa transaction code protection for Kenya and Tanzania

[maziyarpanahi]

Description

Adds strict, context-gated detection for ten-character M-Pesa confirmation codes in Kenyan, Tanzanian, and Swahili billing text. Valid detected codes receive deterministic, validator-safe surrogates that preserve the leading date-encoding character and referential integrity without retaining the original transaction identifier.

Closes #1436.

Type of Change

• New feature (non-breaking change which adds functionality)
• Test addition/improvement

Changes Made

• Added the transaction-code validator and context-gated locale patterns for sw, en_KE, and en_TZ.
• Added a seeded surrogate provider, runtime dispatch, label normalization, and provider-registry aliases for Kenya and Tanzania.
• Added synthetic English and Swahili receipt fixtures covering positive matches, hard negatives, repeated codes, and zero-leakage replacement.
• Rebased onto current master without replacing the existing East African ID and phone locale overlays.
• Restored end-to-end fixture validation through the real Kenya and Tanzania locale routes now supported by current master.

Testing

• I have added tests that prove this feature works
• New and existing unit tests pass locally with my changes
• I have tested this change with different contexts and inputs

Validation completed on the rebased branch:

• .venv/bin/python -m pytest tests/ -q — 6,670 passed, 47 skipped
• Focused validator/provider/receipt regression set — 137 passed
• make format, make lint, make format-check, and make type-check
• Scoped pre-commit hooks, including Ruff, Bandit, hardcoded-secret detection, and merge-conflict detection
• /usr/local/bin/python3 -m build — wheel and source distribution built successfully
• git diff --check

Documentation

• I have added docstrings to new functions/classes
• No user-facing documentation or changelog update is required for this scoped detector addition

Code Quality

• I ran make format, make lint, and make format-check
• I have performed a self-review of my own code
• I have commented the format-preservation behavior where needed
• My changes generate no new warnings
• No dependencies were added

Dependencies

• I have not added any new dependencies

Checklist

• I have read the contributing guidelines
• My commits have clear, descriptive messages
• My commits are organized around this issue only

Related Issues

Closes #1436

Screenshots/Examples

The committed synthetic fixtures cover English and Swahili confirmation lines, ungated specimen/batch hard negatives, and repeated-code receipt copies.

[maziyarpanahi]

Rebased onto the latest master and integrated the M-Pesa provider without displacing the existing East African ID or phone locale overlays. I also restored the end-to-end receipt test to the real Kenya/Tanzania locale routes now supported on master. The full local suite passes (6,670 passed, 47 skipped), all quality/build gates pass, every commit is owner-linked and verified, and the fresh hosted matrix is green on exact head 5c7b483. Ready to merge—thank you!