fix: make script help paths lightweight (#1937)

## Summary

Consolidate the script help/startup fixes so standalone helper commands
can show usage without requiring runtime-only dependencies or generating
files.

## Details

Several helper scripts imported optional packages, evaluated newer
annotations, or started generation before users could inspect CLI usage.
On a fresh checkout, this made common help paths fail on missing
packages such as `cairosvg`, `Pillow`, `freetype-py`, `fontTools`,
`pyphen`, `pyserial`, or on Python 3.9 annotation evaluation. A few
generators also treated `--help` as a normal output argument and wrote
files instead of printing usage.

This change keeps runtime dependencies on the code paths that need them,
handles lightweight help/list commands first, and adds explicit `--help`
handling for generator scripts that previously started work.

## Validation

- `python3 <script> --help` across tracked Python scripts, excluding
`scripts/patch_jpegdec.py` because it is a PlatformIO pre-build hook
rather than a standalone CLI
- `python3 scripts/convert_icon.py` still exits with usage for missing
required arguments
- `python3 lib/EpdFont/scripts/fontconvert_sdcard.py --list-presets`
- `python3 -m py_compile` for the changed scripts

lib/EpdFont/scripts/fontconvert.py

@@ -1,12 +1,10 @@
 #!python3
-import freetype
 import zlib
 import sys
 import re
 import math
 import argparse
 from collections import namedtuple
-from fontTools.ttLib import TTFont
 
 # Force UTF-8 stdout so that `python fontconvert.py … > foo.h` on Windows
 # (default cp1252) doesn't emit UTF-16 LE / replacement chars in the generated
@@ -27,6 +25,9 @@ parser.add_argument("--force-autohint", dest="force_autohint", action="store_tru
 parser.add_argument("--pnum", dest="pnum", action="store_true", help="Use proportional numerals (pnum OpenType feature) instead of default tabular figures. Reduces visual gaps between digits in running prose.")
 args = parser.parse_args()
 
+import freetype
+from fontTools.ttLib import TTFont
+
 GlyphProps = namedtuple("GlyphProps", ["width", "height", "advance_x", "left", "top", "data_length", "data_offset", "code_point"])
 
 font_stack = [freetype.Face(f) for f in args.fontstack]