Fix transfer buffer enforcement and accent-insensitive search

[IgnacioLD]

Transfer buffer fix

Transfer wait times were always showing FGV's min_espera (platform-walk estimate), which happens to equal the real schedule gap. The old code padded tight transfers with fabricated departure/arrival times.

Now:

• Wait is computed from actual hora_llegada / hora_salida times via timeDiffMinutes
• When the real gap < user's buffer, enforceTransferBuffer re-calls planificador-online2 from the transfer station to the destination with hora_salida = arrival + buffer, finding the real next train (not a padded time)
• Cascades through multiple tight transfers; falls back gracefully if re-planning fails
• Duration computed from actual first-departure → last-arrival

Accent-insensitive search

The planner station picker required exact accent matching ("turia" wouldn't find "Túria"). Extracted the normalization logic from SearchViewModel into a shared stripDiacritics() utility in core, now used by both search and planner.

Test plan

• Unit tests for mapper (timeDiffMinutes, addMinutesToTime, planificador journey with real waits)
• App builds and installs
• Verified Benimaclet → Túria: buffer enforcement re-routes to later train when buffer > real gap
• Accent-insensitive search works in planner station picker