fix(knowledge): surface batch reparse failures

[Myang-print]

Description

Batch reparse previously hid per-item submission failures:

• ReparseKnowledge reset a document to pending, then returned success when payload marshaling or task enqueueing failed.
• ProcessKnowledgeListReparse counted failed submissions but always returned nil, so the wrapper task was reported as successful.

This change persists failed document state, propagates submission errors, attempts every item in a batch, and returns an aggregate non-retryable error. The wrapper uses asynq.SkipRetry because automatically retrying a partially submitted batch would clear and reparse documents that were already submitted successfully. Failed documents remain available for an explicit retry.

Regression tests cover the failed state transition, mixed-success aggregation, non-retryable behavior, and the all-success path. The batch-reparse API and its failure semantics are now documented.

There are no API shape, UI, or other breaking changes.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📚 Documentation update
• 🎨 Refactor
• ⚡ Performance improvement
• 🧪 Test
• 🔧 Configuration / Build / CI

Related Issue

Fixes #1651

Testing

• go test ./internal/application/service -count=1 — passes.
• go vet ./internal/application/service — passes.
• go build ./cmd/server — passes.
• golangci-lint run --new-from-rev=upstream/main ./... — passes with 0 issues.
• git diff --check origin/main...HEAD and git diff --check upstream/main...HEAD — pass.
• go test ./... -count=1 — all changed packages pass; the full run is blocked only by unrelated DNS-dependent SSRF tests in internal/datasource, internal/models/chat, internal/models/embedding, and internal/utils. On this WSL/TUN environment, public test hosts such as example.com, open.feishu.cn, and example.openai.azure.com resolve to synthetic 198.18.0.0/15 addresses, which the existing SSRF guard correctly rejects.

Checklist

• git diff --check origin/main...HEAD passes
• Changed source files are formatted
• Targeted tests for the changed packages/components pass
• Diff-scoped lint passes where applicable (for Go: golangci-lint run --new-from-rev=origin/main ./...)
• Full-repository checks were run, or any unrelated/environment-dependent failures are documented above
• Self-reviewed the code
• Added/updated tests covering the change
• Updated related documentation (README, docs/, Swagger annotations, etc.)
• Breaking changes are clearly called out in the description above

Screenshots / Recordings

Not applicable. This change affects backend failure handling and API documentation only; the existing batch-reparse UI is unchanged.