fix-join-without-on-clause-panic - #794

Summary

Fixes #793.

A JOIN with no ON clause crashed plan building with an unrecovered nil pointer dereference in the early-analysis visitor (ast_expand.go), taking down shell, srv and MCP sessions. CROSS JOIN hit the same path because the parser folds it into the plain join string.

Changes:

• earlyanalysis/ast_expand.go: guard the nil On expression before visiting it, matching the convention already used in the other visitors.
• astvisit/param_extract.go: same guard on the one remaining unguarded Condition.On.Accept call.
• astvisit/from_rewrite.go: render a condition-less inner join as CROSS JOIN instead of emitting a dangling ON. Postgres rejects a bare JOIN without ON, sqlite treats it as a cross join, so spelling it out keeps both backends happy. The hoisted-parameter ON ( placeholder ) path is preserved when the planner injects one.

Behaviour: JOIN without ON is now a cross join, as in sqlite, so the join condition can live in WHERE.

Test plan

• New robot scenario Inner Join Without ON Clause Is Treated As Cross Join in the mocked functional suite: joins aws.iam.users to googleadmin.directory.users with the condition in WHERE, with sqlite and postgres input variants. Verified locally that it panics on the unpatched main binary and passes with this change.
• Existing join scenarios (inline LHS joins, cross-cloud fuzzy match, network infra hoisted-ON and data-flow scenarios) pass locally against the patched binary.
• Manual check against the real homebrew provider for the issue's exact query, the no-WHERE form, explicit CROSS JOIN, and the ON 1 = 1 control.
• golangci-lint (pinned 2.5.0) clean on the touched packages; go test green for astanalysis/....

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