fix: add Visibility schema to keypoint template, fix sample data sizes

[shujaatTracebloc]

• Add Visibility column to keypoint schema so client can read visibility flags
• Diversify keypoint labels (person, athlete, dancer) to meet min 2 labels requirement
• Resize keypoint sample images from 256x256 to 448x448 to match target_size
• Resize semantic segmentation sample images and masks to 512x512

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Note

Low Risk
Low risk: template-only changes that add a missing CSV schema column and adjust sample label values; no core ingestion logic is modified.

Overview
Adds an explicit schema for keypoint detection ingestion that includes the Visibility CSV column, and passes it into CSVIngestor so the client can read keypoint visibility flags.

Updates the keypoint detection sample labels_file_sample.csv to use multiple label values (person, athlete, dancer) instead of all person.

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[LukasWodka]

👋 Heads-up — Code review queue is at 10 / 8

Above the WIP limit. The team convention is to review existing PRs before opening new work.

Open PRs currently in Code review (oldest first):

• data-ingestors#67 — feat: support BACKEND_TOKEN auth, remove hardcoded backend credentials · author: @saadqbal · no reviewer assigned
• docs#14 — docs: migrate join-use-case API examples to snake_case (0.7.0) · author: @divyasinghds · no reviewer assigned
• docs#26 — docs: add "How training works" page · author: @divyasinghds · no reviewer assigned
• docs#4 — docs: switch install to extras syntax for tracebloc_package 0.6.33 · author: @LukasWodka · reviewer: @saadqbal
• start-training#10 — ci: add WIP-limit-check caller workflow · author: @LukasWodka · no reviewer assigned
• start-training#6 — chore: add PR template + customer bump + stale auto-close · author: @LukasWodka · no reviewer assigned
• start-training#9 — ci: add kanban closure-routing caller workflow · author: @LukasWodka · no reviewer assigned
• tracebloc-py-package#117 — TEST: trigger WIP-limit-check (do not merge — will close shortly) · author: @saadqbal · no reviewer assigned
• tracebloc-py-package#127 — fix: restrict semantic segmentation to crossentropy in loss_function (#126) · author: @aptracebloc · reviewer: @shujaatTracebloc

Pull from review before opening new work. (This is a nudge from the kanban WIP check, not a block.)

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