v0.2.9 — Ekadashi tithi-kshaya fix

Fixed

• compute_ekadashis: Kshaya Ekadashis (where tithi 11/26 never spans sunrise within a lunar month) are now correctly resolved to the preceding Dashami day per Smarta convention, instead of being silently dropped. Prabodhini Ekadashi 2026 (Nov 20) was the motivating case.
• compute_ekadashis: Lunar-month labels are now correct. The old sankranti-anchored ±20-day search sometimes returned Ekadashis with the wrong lunar_month when search windows overlapped (e.g., Jan 29 2026 was returned as "Pausha Putrada" when it is actually "Jaya"). The new Amant-bounded search prevents this class of mis-labeling.

Unchanged

• Vaishnava Ekadashi rule (Dashami-at-Arunodaya shift) is preserved.
• Festival resolution, panchang batch, Sankranti, and all other APIs are unchanged.

Tests

• Added regression tests for Prabodhini 2026 and correct Magha Shukla labeling.
• Full suite: 119 Python tests + 73 Rust tests, all passing.