Harmonized time signature, metronome mark and clef positioning.

Three critical LilyPond overrides:

    \override MetronomeMark.break-align-symbols = #'(left-edge)
    \override TimeSignature.break-align-symbol = #'left-edge
    \override TimeSignature.space-alist.clef = #'(extra-space . 0.5)

Note that these two overrides alone give the correct visual output:

    \override MetronomeMark.break-align-symbols = #'(left-edge)
    \override TimeSignature.break-align-symbol = #'left-edge

... but that LilyPond then complains with ...

    programming error: No spacing entry from Item to `clef'

... many times in the LilyPond log. The solution is to add ...

    \override TimeSignature.space-alist.clef = #'(extra-space . 0.5)

... or equivalent, which seems to provide a spacing entry explaining to
LilyPond how much distance to insert from time-signature-left-edge to
clef-left-edge.

Note that you can tweak this last pair to insert visible whitespace between the
system start bar and all clefs without causing time signatures or metronome
marks to move.