LLM-30062 remove dead LightAgent

LightAgent is superseded by the ACP-based agents and unmaintained. In
released IDEs it was reachable only via the nightly-only
llm.code.lightAgent.enabled registry key, which defaults to disabled,
yet it kept a 68-file subsystem, ten registry keys, a tool window and a
message-part renderer alive.

It was, however, not dead everywhere: isLightAgentEnabled() also
returned true in any headless environment, so the agent was live in
evaluation runs. The LIGHT_AGENT SWE-benchmark runner and its evaluation
config go away with it, as does GrazieQuotaSpentTest, which selected
LightAgent deliberately for koog-integration coverage and whose own
comment scheduled it for removal alongside the agent.

ProjectFile and ProjectStructureContext are moved into plugins/llm/vcs
rather than deleted, because the .gitignore directory-structure
retriever renders through them. Their @Deprecated notes pointed at
PathContext, which lived in the deleted package, so the notes are
dropped.

The agent_LightAgent entry in ChatModeIdValidator's FUS allowlist is
kept intentionally so historical events keep validating.

(cherry picked from commit 728effd91fd4373cd12fda108e249c56af32cac3)
(cherry picked from commit 3140fee3f0d743948dd5ef951a9aaca626ce1f25)

IJ-MR-217492

GitOrigin-RevId: 4d781b66ad99d5937f06c4c920e855ed35492018

plugins/evaluation-plugin/languages/evaluationconfig/codegeneration/java_swe_light_agent.json

@@ -1,35 +0,0 @@
-{
-  "projectPath": "../ml-eval/jackson-core",
-  "repository": "https://github.com/fasterxml/jackson-core",
-  "revision": "f1dc3c512d211ae3e14fb59af231caebf037d510",
-  "outputDir": "bin/ml-eval-code-generation-swe-java-output",
-  "strategy": {
-    "instanceId": "fasterxml__jackson-core-1142",
-    "runner": "LIGHT_AGENT"
-  },
-  "fileDataset": {
-    "url": "remote:https://huggingface.co/datasets/JetBrains/eval_plugin/resolve/main/code-generation-swe/java/java_swe_bench.json"
-  },
-  "interpret": {
-    "saveLogs": true,
-    "sessionProbability": 1.0,
-    "sessionSeed": null,
-    "sessionsLimit": 400,
-    "filesLimit": 100,
-    "order": "LINEAR",
-    "trainTestSplit": 70,
-    "registry": "",
-    "iterationCount": 1
-  },
-  "reports": {
-    "evaluationTitle": "Default",
-    "sessionsFilters": [],
-    "comparisonFilters": []
-  },
-  "language": "Java",
-  "actions": {
-    "evaluationRoots": [
-      "."
-    ]
-  }
-}

plugins/evaluation-plugin/languages/evaluationconfig/insight/kotlin.json

@@ -55,8 +55,6 @@
       "plugins/llm/chat/src/com/intellij/ml/llm/core/chat/ui/chat/context/popup/promotion/PopupPromotableFeature.kt",
       "plugins/llm/chat/src/com/intellij/ml/llm/core/chat/ui/chat/input/AIAssistantInput.kt",
       "plugins/llm/chat/src/com/intellij/ml/llm/tasks/AITaskEventHistoryStorage.kt",
-      "plugins/llm/codeGeneration/src/com/intellij/ml/llm/codeGeneration/lightAgent/LightAgent.kt",
-      "plugins/llm/codeGeneration/src/com/intellij/ml/llm/codeGeneration/lightAgent/context/FindTextUtils2.kt",
       "plugins/llm/codeGeneration/src/com/intellij/ml/llm/codeGeneration/multifile/core/part/LlmPatchMessagePartFactory.kt",
       "plugins/llm/core/src/com/intellij/ml/llm/core/chat/ui/chat/input/chatModeSelector/AIAssistantNewChatModeService.kt",
       "plugins/llm/core/src/com/intellij/ml/llm/core/models/LlmProfileService.kt",