fix: filter log messages without container prefixes

[paknahad]

Summary

• filter log visibility against a buffered message/status field instead of the rendered line
• keep container prefixes visible while preventing prefix-only matches from showing lines
• document the log view's separate display and filter targets

Tests

• go test ./internal/ui
• go test ./...
• go vet ./...
• staticcheck ./...
• DOCS_GATE_SOURCE_ROOT=internal DOCS_GATE_EXT=go bash scripts/docs-gate.sh

make ci could not run locally because this host Docker CLI does not support docker compose.

Closes #37

[paknahad]

Cycle cost: $0.00. Total on this PR: $0.00.