feat(job-search): extract keywords from LLM match call instead of heuristics

Piggybacks keyword extraction onto the existing CV-to-job LLM call —
no extra API calls. The system prompt now instructs the model to return
8-12 English job-search terms (job titles, technologies, skills, domains)
in a new `keywords` field alongside the existing score/summary fields.

Keywords flow: LLM JSON → JobMatchResponse.Keywords → CreateJobSearchTokenRequest →
JobSearchTokenEntity.Keywords (stored comma-separated) → JobSearchSessionEntity.Keywords
(copied at session-creation time, no RAG call needed).

Changes:
- Add Keywords to JobMatchResponse, CreateJobSearchTokenRequest, JobSearchTokenEntity
- IJobTokenService.CreateTokenAsync now accepts IReadOnlyList<string> keywords
- JobTokenService: store keywords on token; TriggerStartAsync reads token.Keywords
  instead of fetching CV text from RAG — removes IRagApiClient dependency
- Remove heuristic ExtractKeywords method
- Migration AddKeywordsToJobSearchTokens: adds Keywords column to cvSearch.JobSearchTokens
- Migration UpdateCvMatchSystemPromptKeywords: updates ai.cv-match.system-prompt seed
  to include keywords in the JSON shape

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/cv-matcher-api/Services/Contracts/IJobTokenService.cs

@@ -12,12 +12,13 @@ public interface IJobTokenService
     /// <param name="cvDocumentId">Identifier of the indexed CV document.</param>
     /// <param name="email">Email address of the user who will receive the results.</param>
     /// <param name="language">Preferred language for result emails (e.g. <c>"en"</c>, <c>"ro"</c>).</param>
+    /// <param name="keywords">Job search keywords extracted by the LLM during the match call.</param>
     /// <param name="ct">Cancellation token.</param>
     /// <returns>
     /// The generated token ID to embed in the one-click job search link,
     /// or <c>null</c> when no job providers are currently enabled (link should be suppressed).
     /// </returns>
-    Task<string?> CreateTokenAsync(string cvDocumentId, string email, string language, CancellationToken ct);
+    Task<string?> CreateTokenAsync(string cvDocumentId, string email, string language, IReadOnlyList<string> keywords, CancellationToken ct);
 
     /// <summary>
     /// Validates the token and, if valid, marks it as used and creates a <c>Pending</c> job search session.