fix(core): reject blank URIs and empty template captures

[liyifan9642-creator]

Summary

Fixes #1085.

PathSegmentTemplateMatcher.match("") currently matches {id} with id = "", allowing a blank resources/read URI to reach a template handler.

• Reject blank incoming URIs after the existing length check.
• Reject empty variable captures without rejecting empty literal segments, such as those in file:///report.txt.
• Update the matching contract and replace the test that pinned empty-URI captures.
• Add regression coverage for blank URIs, empty variable segments, valid file URIs, percent-encoded whitespace, and the literal root path.
• Add an in-memory client/server test verifying that blank resource URIs return RESOURCE_NOT_FOUND and do not invoke the template handler.

No public API or tracked build configuration changes.

Verification

Before the production fix, the matcher tests failed in the two expected cases, and the new client/server regression test failed because no exception was thrown.

After the fix:

• :kotlin-sdk-core:jvmTest: 258 tests passed.
• :integration-test:jvmTest --tests '*ServerResourceTemplateTest': 9 tests passed.
• :kotlin-sdk-core:ktlintCheck and :integration-test:ktlintCheck: passed.
• :kotlin-sdk-core:checkKotlinAbi: passed, including the multiplatform ABI comparison.
• git diff --check: passed.

The core Detekt task completed successfully but reported 107 compiler errors during analysis, so its type-resolved analysis accuracy was limited. Local validation used an external Gradle init script to resolve plugins through a reachable mirror; dependency versions and tracked build files were unchanged.

[jetbrains-air]

Looks good to me — approving, thanks!

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