Merge curated fork work: 12 new diagram types, icons, export, onboarding v2

Imports the substantive work from the aristide/diagram-design fork (PR #9)
as a curated set:

- 12 new diagram types with reference docs: radar, bar, line, gantt,
  scatter, it-state, high-level, process, medallion, data-flow,
  dp-integration, dp-security-matrix (26 types total)
- 86-icon monochrome IT/cloud primitive, build script, and gallery
- /diagram-design:export command with PNG/SVG export reference
- Onboarding v2: URL, skill, and folder design-token sources
- Mandatory connector rules (orthogonal elbows, label gaps, fanned
  attach points, bridge crossings) + architecture/ER connector upgrades
- Series palette tokens for multi-series chart types
- THIRD_PARTY_LICENSES.md covering Tabler, Simple Icons, log-z, Devicon

Not taken from the fork: plugin-manifest identity changes, the client-brand
takeover of style-guide.md, and client-branded example files. The six
affected type examples were regenerated in the neutral editorial skin with
generic content, and their README screenshots recaptured. Reference docs
for those types were rewritten to semantic tokens and typography roles.

Version: 1.0.0 -> 2.0.0.

Co-authored-by: Aristide <mendoo.aristide@gmail.com>

scripts/fix-mojibake.py

@@ -0,0 +1,61 @@
+"""Replace mojibake sequences in UTF-8 files with their original characters.
+
+The repo had a few files saved by a tool that interpreted UTF-8 as cp1252 and
+re-saved as UTF-8, producing classic mojibake (em-dash --> 'â€"', section sign
+--> '§', right arrow --> 'â†'', etc.). This script rewrites those sequences
+in-place without touching legitimately-encoded UTF-8 elsewhere in the file.
+"""
+import sys
+
+PAIRS = [
+    ('—', '—'),  # em-dash
+    ('–', '–'),  # en-dash
+    ('’', '’'),  # right single quote
+    ('‘', '‘'),  # left single quote
+    ('“', '“'),  # left double quote
+    ('”', '”'),  # right double quote
+    ('…', '…'),  # horizontal ellipsis
+    ('•', '•'),  # bullet
+    ('→', '→'),  # right arrow
+    ('↑', '←'),  # left arrow
+    ('↑', '↑'),  # up arrow (same prefix collision - rare)
+    ('↓', '↓'),  # down arrow
+    ('≤', '≤'),  # less-than-or-equal
+    ('≥', '≥'),  # greater-than-or-equal
+    ('×',       '×'),  # multiplication sign
+    ('÷',       '÷'),  # division sign
+    ('§',       '§'),  # section sign
+    ('°',       '°'),  # degree
+    ('½',       '½'),  # one-half
+    ('«',       '«'),  # «
+    ('»',       '»'),  # »
+    ('©',       '©'),  # ©
+    ('®',       '®'),  # ®
+]
+
+
+def fix(path: str) -> int:
+    with open(path, 'rb') as f:
+        raw = f.read()
+    had_bom = raw.startswith(b'\xef\xbb\xbf')
+    if had_bom:
+        raw = raw[3:]
+    text = raw.decode('utf-8')
+    n = 0
+    for bad, good in PAIRS:
+        if bad in text:
+            n += text.count(bad)
+            text = text.replace(bad, good)
+    if n == 0 and not had_bom:
+        print(f'{path}: no mojibake found')
+        return 0
+    with open(path, 'w', encoding='utf-8', newline='\n') as f:
+        f.write(text)
+    note = f' (also stripped BOM)' if had_bom else ''
+    print(f'{path}: replaced {n} sequence(s){note}')
+    return n
+
+
+if __name__ == '__main__':
+    for p in sys.argv[1:]:
+        fix(p)