collect: add call tree text and JSON for all profiles

[AlexsanderHamir]

Summary

• Collect pprof -tree\ text reports for every processed profile under .prof//call_trees//.txt, using the same flags as hotspots (-cum -nodefraction=0 -edgefraction=0).
• Export structured call-graph JSON (all nodes with flat/cum/% plus caller→callee edges) to .prof//call_trees//.json\ via the in-process parser.
• Wire both artifacts into auto and manual collection paths.

Profile artifact refactor (follow-up commits on this branch)

• Unified pprof text runner — \PprofTextReportArgs\ +
  unPprofReport\ replace duplicate -top\ / -tree\ helpers.
• Parse-once bundle — \parser.ProfileBundle\ aggregates flat/cum and call graph in one pipeline pass; JSON emission reads from the bundle instead of re-parsing.
• Artifact catalog — \ProfileArtifact\ registry with \Required\ / \BestEffort\ policies drives \processOneProfile\ and \�mitProfileArtifacts; PNG remains best-effort with warn-and-continue.

Test plan

• \go test ./... -count=1\
• \golangci-lint\ clean
• \�ngine/collect\ tests assert catalog order, required failures, and best-effort PNG skip
• \parser\ tests cover \BundleFromPath, synthetic stack edges, and fixture JSON round-trip
• Manual spot-check: \prof auto\ on a benchmark and confirm .prof//\ artifact tree unchanged (hotspots, call_trees, call_graphs)