Move Darklang to concluded projects list as Darklang Classic

[Copilot]

Darklang is no longer developing a structural editor and has transitioned to being a text-based language. Instead of completely removing it from the list, this PR moves it to the concluded/inactive projects section to preserve its historical significance in the structural editing space.

Changes made:

1. Moved Darklang to concluded/inactive projects - Added as "Darklang Classic" (2017-2024) to distinguish it from the current text-based version
2. Preserved sponsorship reference - Kept "Sponsored by Dark" in the Resources section as it remains relevant for historical context
3. Added clarifying description - Notes the transition from structural to text-based editing

The entry now appears in the concluded projects table with appropriate context about its role in structural editor history before the platform pivoted to text-based editing.

Fixes #37.

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[yairchu]

@copilot as suggested in #37 (comment) :

it should be on the concluded/inactive list and should specify "Darklang Classic".

So need to also add it to that list, and also no need to remove the "sponsored by Dark" comment.

[Copilot]

@copilot as suggested in #37 (comment) :

it should be on the concluded/inactive list and should specify "Darklang Classic"...

Done! I've moved Darklang to the concluded/inactive projects list as "Darklang Classic" with the time period 2017-2024 and restored the "Sponsored by Dark" reference in the Resources section. The changes preserve the table structure and clarify that this was the structural editor version before the transition to text-based editing. (commit 09feee8)