feat: add argument parsing and plain output flag

- Add command-line argument parsing using `go-arg` library
  - Define `Args` struct with `Plain` flag (`-p/--plain`)
  - Implement `Description()` method for program help text
  - Parse arguments in `main()` before loading Bible data
- Add `-p/--plain` flag to output plain text without chapter name or
verse numbers
  - Conditionally skip header formatting when flag is set
- Update `.gitignore` to exclude `bibel` binary
- Remove obsolete `bibel_date` binary and `bookmark.toml` file
- Update `CHANGELOG.md` with version 1.1.0 entry documenting new
features
- Add `github.com/alexflint/go-arg` and `go-scalar` dependencies to
`go.mod` and `go.sum`

feat: replace bookmark-based progression with date-based daily verses

- Remove bookmark persistence system and TOML dependency
  - Delete `internal/bookmark.go` and all bookmark manager logic
  - Remove `github.com/pelletier/go-toml/v2` from `go.mod`
  - Delete `test/bookmark.toml` and `invalid_bookmark.toml`
- Add date-based progression (`internal/dateprogression.go`)
  - Calculate reading position from day of year (12 verses per day)
  - Wrap yearly through all four Gospels (3779 total verses)
  - Apply lookahead rule when fewer than 12 verses remain in chapter
- Update `cmd/bibel.go` to use `DateProgression` instead of
`BookmarkManager`
  - Display today's verses without reading or writing any bookmark file
  - Support test dates via `GOOSE_TEST_DATE` environment variable
- Revise `README.md` to document date-based algorithm and usage
- Add `CHANGELOG.md` with version 1.0.0 and complete migration notes
- Clean up `.gitignore` (remove editor/IDE and old_code.ml entries)
- Keep `old_code.ml` as reference for original OCaml implementation

First commit