fix(codemode): truncate structured results structurally and keep the call log out of model context (#2224)

* fix(codemode): truncate structured results structurally and keep the call log out of model context

truncateResult shrinks an oversized value in place, largest values first, so
the model always receives valid JSON of the original shape. The MCP servers
shape results on the host with it instead of slicing pretty-printed JSON. The
Code Mode tool gains a toModelOutput that drops the durable calls log from
what the model sees; the persisted output keeps it for UIs. Compaction
summaries serialize structured tool outputs as JSON.

Closes #2009, #2143, #2182, #2138.

* fix(codemode): make structural truncation budget-honest and keep logs/calls bounded for the model

Review findings: the array prefix search assumed a monotone predicate and
could drop every element when the whole array fit; the object fallback marker
was unbounded, so a long list of small records overshot its slot and fell back
to the string slice this PR removes. Shrinking now guarantees its budget by
construction: every child is owed a floor, containers only drop children when
the floors cannot fit, and markers are clipped to the room left. A real key
named like the marker is no longer shadowed.

The MCP servers apply the response budget to the emitted text (pretty only
while it fits). toModelOutput bounds logs, renders BigInt, and never throws
on a cycle. browser_execute drops calls from its model projection too.

* fix(codemode): linear object shrinking, bounded omitted-key note, bounded browser logs

shrinkObject tracks costs incrementally instead of rescanning every entry per
drop, and the omitted-key note is allocated and shrunk like any other value so
it can never overshoot its slot. browser_execute bounds logs in its model
projection like the codemode tool does.