1.2.10

yacron2 now parses cron expressions itself. This release retires the
third-party crontab (parse-crontab) library in favor of a small,
stdlib-only engine that lives in the tree -- so the scheduler owns the one
piece of syntax every job depends on, the dialect is documented and tested
where it is implemented, and the install carries one dependency fewer.
Compatibility is not aspirational: it is pinned by golden vectors recorded
from the old library across 180+ expressions and fixed instants (DST
transitions, leap days, month/year boundaries, the year cap, ambiguous
fall-back folds). Nothing changes for existing configs -- the dialect, the
timezone model, and the strictly-future fire semantics are all preserved
vector-by-vector.

• yacron2/cronexpr.py: the built-in cron engine. A new CronTab class
  parses the crontab dialect yacron2 has always accepted (5/6/7 fields,
  ranges, steps including bare-start 5/15, lists, case-insensitive
  jan/mon names, 0-7 weekdays with 6-0 wrap, L-last-day and
  L5-last-Friday forms, @-nicknames) and answers the scheduler's two
  questions: next() (strictly future, DST-correct across UTC-offset
  changes, capped at the 2099 horizon so dead schedules drop from the index)
  and test(). A stdlib-only leaf module -- calendar and datetime, no
  third-party imports.

• The crontab dependency is dropped. Removed from pyproject.toml and
  every import site (config.py, cron.py, crontabs.py, dagrun.py,
  prometheus.py); classic crontab-file loading and YAML schedule strings
  now share the same in-house engine, so both formats still accept identical
  expressions.

• Golden-vector compatibility harness. tests/gen_cron_golden.py
  records next()/test() answers from the original parse-crontab library
  into tests/data/cron_golden.json; tests/test_cronexpr.py replays them
  against the new engine so any behavioral drift fails the suite. This is
  the proof that "behavior-compatible" is a fact, not a hope.

• mergedicts reimplemented. The config defaults-merge helper is
  rewritten with the identical semantics -- dicts merge recursively, an empty
  YAML section (None) never wipes a populated default, environment and
  secrets lists merge by key/name, sentry fingerprint replaces rather
  than appends, and all other lists concatenate -- and now returns a dict
  directly, retiring the dict(mergedicts(...)) wrappers at every call site.

• Dashboard accessibility pass. The web UI gains an interface font
  toggle (the terminal monospace, or a proportional sans "reader mode" for
  easier reading, with logs and cron strings kept monospace either way),
  app-level color-vision palettes (deutan / tritan status-color remaps,
  status glyphs always distinct too), whole-UI zoom, and a
  reduce-motion switch, each reachable from Settings and the command
  palette and persisted across sessions.

• Docs. The "Schedules and Timezones" wiki page now documents the full
  dialect the engine owns -- the day-of-month-AND-day-of-week rule (Friday
  the 13th, deliberately kept over Vixie's OR), the L forms, the
  1970-2099 year horizon -- and Installation, Migration-from-yacron,
  Classic-Crontabs, Architecture-and-Internals, and the README are updated to
  point at the built-in engine instead of the removed library.

Full Changelog: 1.2.9...1.2.10