Add LinkedIn Post Formatter skill and LinkedIn Post Writer agent 🤖🤖🤖 (#1392)

* feat(skills,agents): add LinkedIn post formatter skill and writer agent

Add self-contained LinkedIn post formatting skill with Unicode bold/italic
character mapping and engagement-optimized post structure patterns.
Add LinkedIn Post Writer agent for transforming raw content into
copy-paste-ready LinkedIn posts. No external service dependencies.

* fix: address Copilot review comments on PR #1392

- Correct Unicode range header to include digit range (U+1D7EC–U+1D7F5)
- Add explicit instruction to load references/unicode-charmap.md
- Fix LinkedIn casing in README.agents.md (Linkedin → LinkedIn)

* fix: use display name for LinkedIn agent to preserve brand casing

The name field now uses 'LinkedIn Post Writer' instead of the slug
format, ensuring the auto-generated README table shows correct casing.

---------

Co-authored-by: Shailesh Mishra <shaileshmishra@example.com>

skills/linkedin-post-formatter/references/unicode-charmap.md

@@ -0,0 +1,53 @@
+# Unicode Character Map Reference
+
+Full mapping tables for LinkedIn Unicode formatting. Load this file when generating posts to ensure correct character conversion.
+
+## Sans-Serif Bold (Letters: U+1D5D4 – U+1D607; Digits: U+1D7EC – U+1D7F5)
+
+```
+A → 𝗔  B → 𝗕  C → 𝗖  D → 𝗗  E → 𝗘  F → 𝗙  G → 𝗚  H → 𝗛  I → 𝗜  J → 𝗝
+K → 𝗞  L → 𝗟  M → 𝗠  N → 𝗡  O → 𝗢  P → 𝗣  Q → 𝗤  R → 𝗥  S → 𝗦  T → 𝗧
+U → 𝗨  V → 𝗩  W → 𝗪  X → 𝗫  Y → 𝗬  Z → 𝗭
+
+a → 𝗮  b → 𝗯  c → 𝗰  d → 𝗱  e → 𝗲  f → 𝗳  g → 𝗴  h → 𝗵  i → 𝗶  j → 𝗷
+k → 𝗸  l → 𝗹  m → 𝗺  n → 𝗻  o → 𝗼  p → 𝗽  q → 𝗾  r → 𝗿  s → 𝘀  t → 𝘁
+u → 𝘂  v → 𝘃  w → 𝘄  x → 𝘅  y → 𝘆  z → 𝘇
+
+0 → 𝟬  1 → 𝟭  2 → 𝟮  3 → 𝟯  4 → 𝟰  5 → 𝟱  6 → 𝟲  7 → 𝟳  8 → 𝟴  9 → 𝟵
+```
+
+## Sans-Serif Italic (U+1D608 – U+1D63B)
+
+```
+A → 𝘈  B → 𝘉  C → 𝘊  D → 𝘋  E → 𝘌  F → 𝘍  G → 𝘎  H → 𝘏  I → 𝘐  J → 𝘑
+K → 𝘒  L → 𝘓  M → 𝘔  N → 𝘕  O → 𝘖  P → 𝘗  Q → 𝘘  R → 𝘙  S → 𝘚  T → 𝘛
+U → 𝘜  V → 𝘝  W → 𝘞  X → 𝘟  Y → 𝘠  Z → 𝘡
+
+a → 𝘢  b → 𝘣  c → 𝘤  d → 𝘥  e → 𝘦  f → 𝘧  g → 𝘨  h → 𝘩  i → 𝘪  j → 𝘫
+k → 𝘬  l → 𝘭  m → 𝘮  n → 𝘯  o → 𝘰  p → 𝘱  q → 𝘲  r → 𝘳  s → 𝘴  t → 𝘵
+u → 𝘶  v → 𝘷  w → 𝘸  x → 𝘹  y → 𝘺  z → 𝘻
+```
+
+## Sans-Serif Bold Italic (U+1D63C – U+1D66F)
+
+```
+A → 𝘼  B → 𝘽  C → 𝘾  D → 𝘿  E → 𝙀  F → 𝙁  G → 𝙂  H → 𝙃  I → 𝙄  J → 𝙅
+K → 𝙆  L → 𝙇  M → 𝙈  N → 𝙉  O → 𝙊  P → 𝙋  Q → 𝙌  R → 𝙍  S → 𝙎  T → 𝙏
+U → 𝙐  V → 𝙑  W → 𝙒  X → 𝙓  Y → 𝙔  Z → 𝙕
+
+a → 𝙖  b → 𝙗  c → 𝙘  d → 𝙙  e → 𝙚  f → 𝙛  g → 𝙜  h → 𝙝  i → 𝙞  j → 𝙟
+k → 𝙠  l → 𝙡  m → 𝙢  n → 𝙣  o → 𝙤  p → 𝙥  q → 𝙦  r → 𝙧  s → 𝙨  t → 𝙩
+u → 𝙪  v → 𝙫  w → 𝙬  x → 𝙭  y → 𝙮  z → 𝙯
+```
+
+## Visual Symbols
+
+```
+Section divider: ━━━━━━━━━━━━━━━━━━━━━━
+Diamond bullet:  ◈
+Bullseye bullet: ◎
+Down arrow:      ↓
+Right arrow:     →
+Sub-item arrow:  ↳
+Repost icon:     ♻️
+```