fix: standardize BSD-clear license files

[Eikix]

This standardizes the repo on the strict BSD 3-Clause Clear license text.
It removes the old patent addendum from the root license, deletes the duplicate sdk/rust-sdk/LICENSE file to avoid future drift, and repoints the SDK README license link to the root license.
No behavior changes.

[Eikix]

@Mergifyio queue

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-03-19 15:48 UTC · Rule: main
• ✅ Checks passed · on draft merge queue: embarking main (e7b2ee7) and #2136 together #2139
• ✅ Merged — 2026-03-19 17:17 UTC · at 73bd7f5f85a661898dff18126e0f65c0e9cbb5ad

This pull request spent 1 hour 28 minutes 51 seconds in the queue, including 27 minutes 12 seconds running CI.

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• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • fix: standardize BSD-clear license files #2136
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  • fix: standardize BSD-clear license files #2136
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  • fix: standardize BSD-clear license files #2136
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  • fix: standardize BSD-clear license files #2136
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