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_sdcard.py

@@ -22,7 +22,8 @@ Usage:
 
 """
 
-import freetype
+from __future__ import annotations
+
 import struct
 import sys
 import os
@@ -31,8 +32,6 @@ import math
 import argparse
 from collections import namedtuple
 
-from fontTools.ttLib import TTFont
-
 from cpfont_version import CPFONT_VERSION
 
 # --- Unicode interval presets ---
@@ -252,6 +251,8 @@ def extract_kerning_fonttools(font_path, codepoints, ppem):
     codepoints.  Values are scaled from font design units to integer
     pixels at ppem.
     """
+    from fontTools.ttLib import TTFont
+
     font = TTFont(font_path)
     units_per_em = font['head'].unitsPerEm
     cmap = font.getBestCmap() or {}
@@ -402,6 +403,8 @@ def extract_ligatures_fonttools(font_path, codepoints):
     Returns list of (packed_pair, ligature_codepoint) for the given codepoints.
     Multi-character ligatures are decomposed into chained pairs.
     """
+    from fontTools.ttLib import TTFont
+
     font = TTFont(font_path)
     cmap = font.getBestCmap() or {}
 
@@ -514,6 +517,8 @@ def extract_ligatures_fonttools(font_path, codepoints):
 
 def rasterize_font_style(fontfile, size, intervals, style_id=0, force_autohint=False):
     """Rasterize all glyphs for one font style. Returns StyleRasterData."""
+    import freetype
+
     style_names = {0: "regular", 1: "bold", 2: "italic", 3: "bolditalic"}
     style_label = style_names.get(style_id, str(style_id))