feat: Update existing spellcheck configuration with documentation terms

- Add custom documentation-specific terms to .github/actions/spelling/expect/expect.txt:
  - doctrees (Sphinx documentation tree structures)
  - graphviz (diagram generation tool for architecture diagrams)
  - iseconds (time unit reference for performance metrics)
  - pandoc (document conversion tool used in build process)
- Rename spelling2.yml to spelling.yml for standard workflow naming
- Remove redundant spellcheck files (used existing check-spelling workflow)
- Terms added in proper alphabetical order to maintain file organization

The existing check-spelling workflow is comprehensive with SARIF reporting,
PR comment management, and extensive dictionary support from cspell-dicts.
These additions ensure documentation-specific terms are properly recognized.

Author: vinod0m

.github/actions/spelling/expect/expect.txt

@@ -341,6 +341,7 @@ DBGOUTPUT
 dbh
 dblclk
 DBUILD
+doctrees
 Dcd
 DColor
 DCOMMON
@@ -696,6 +697,7 @@ GMEM
 Goldmine
 gonce
 goutput
+graphviz
 GREENSCROLL
 Grehan
 Greyscale
@@ -831,6 +833,7 @@ INVALIDATERECT
 Ioctl
 ipch
 ipsp
+iseconds
 iterm
 itermcolors
 itf
@@ -1209,6 +1212,7 @@ PACKAGEVERSIONNUMBER
 PACKCOORD
 PACKVERSION
 pacp
+pandoc
 pagedown
 pageup
 PAINTPARAMS