refactor(markdown): move template settings from export dialog to settings panel

[tangcent]

Move the template file, URL, inline editor, copy-default-template button, and language selector from the Markdown export dialog to the persistent Markdown settings tab. These are configuration preferences that users set once, not per-export choices, so they belong in Settings rather than cluttering the export action panel.

The export dialog now only shows Output Directory and File Name — the per-export essentials.

[github-actions]

📦 Plugin has been packaged for this PR. You can download easy-api-3.1.8.252.0.zip from the GitHub Actions workflow run by clicking on the "Artifacts" dropdown.

[codecov]

Codecov Report

❌ Patch coverage is 58.09524% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.713%. Comparing base (886f7f7) to head (5f95b38).

Files with missing lines	Patch %	Lines
.../easyapi/channel/markdown/MarkdownSettingsPanel.kt	53.846%	35 Missing and 7 partials ⚠️
...ngcent/easyapi/channel/markdown/MarkdownChannel.kt	80.000%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##            master      #747       +/-   ##
=============================================
- Coverage   66.759%   66.713%   -0.046%     
=============================================
  Files          427       429        +2     
  Lines        24184     24208       +24     
  Branches      5908      5916        +8     
=============================================
+ Hits         16145     16150        +5     
- Misses        5800      5810       +10     
- Partials      2239      2248        +9     

Flag	Coverage Δ
unittests	66.713% <58.095%> (-0.046%)	⬇️

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Files with missing lines	Coverage Δ
...gcent/easyapi/channel/markdown/MarkdownSettings.kt	100.000% <100.000%> (ø)
...ngcent/easyapi/channel/markdown/MarkdownChannel.kt	72.727% <80.000%> (+3.456%)	⬆️
.../easyapi/channel/markdown/MarkdownSettingsPanel.kt	53.846% <53.846%> (ø)

... and 2 files with indirect coverage changes

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[github-actions]

📦 Plugin has been packaged for this PR. You can download easy-api-3.1.8.252.0.zip from the GitHub Actions workflow run by clicking on the "Artifacts" dropdown.

[github-actions]

📦 Plugin has been packaged for this PR. You can download easy-api-3.1.8.252.0.zip from the GitHub Actions workflow run by clicking on the "Artifacts" dropdown.