[KEYWORD] Add break / continue / pass mappings

[alphacrack]

DEVNAGIRI_KEYWORD_MAP has no mappings for break, continue, or pass — loops cannot be exited early and empty blocks cannot be written.

Suggested starting points (native speakers, please improve!):

• रोकू → break
• आगू बढू → continue (multi-word: must be ordered before any single-word prefix entries)
• छोड़ू → pass

Steps:

1. Add mappings in maithili_dsl/transpiler/mappings.py
2. Word-boundary + string-literal regression tests in tests/test_transpile.py
3. Update the README keyword table and add/extend an example in examples/
4. If the linter's structure whitelist (linter.py:38) needs the new words on :-lines, update it too

Depends on nothing; pairs nicely with जबतक/while (#8).

Good first issue — mostly data + tests. Please propose word choices in a comment before opening the PR so speakers can weigh in.