fix: bound log memory usage

[maful]

Problem

Log history was limited by line count but not byte size. A process could retain nearly 20 GiB of output per pane. Filtering one accepted 1 MiB line for a one-character query also created about 24 MiB of occurrence spans.

Changes

• Truncate displayed lines at 64 KiB while continuing to drain oversized records.
• Limit queued output to 256 events and report lines dropped during sustained bursts.
• Enforce 16 MiB per-process and 64 MiB global retained-log budgets.
• Cap navigation spans at 10,000 while retaining the exact occurrence count.
• Limit viewport materialization to 8 MiB and show omission markers.

The streaming reader also prevents oversized lines from blocking a managed process.