Emit the v2 L1 tree: `can://` ids, `span`, `source`, `body{}` call nodes

[lamwassi]

Is your feature request related to a problem? Please describe.

The Go analyzer serializes the v1 shape. L1 is the structural keystone of the v2
migration: it introduces the additive containment tree and every Group A identity
decision the later levels build on. Do L1 first and get the symbol-table gate green
before touching the L2 call graph. The parser/resolver stay; only the emission layer
changes (golden rule: replace what serializes, keep what computes).

Describe the solution you'd like

• application.id = can://go/<app>, <app> = --app-name (default: input dir base name)
• Durable can:// ids on module/type/callable; signatureOf() is the last segment
• span: {start:[l,c], end:[l,c], bytes:[from,to]} with UTF-8 byte offsets; drop flat start_line/end_line
• source emitted once per module; drop per-callable code
• type.kind ∈ struct|interface|alias|defined; methods grouped under receiver type's callables{}
• base_types[] = embedded ids, interfaces[] = computed structural satisfaction
• body{} holds call nodes with callee:null, typed is_goroutine/is_deferred; closures nest in callables{}

Describe alternatives you've considered

Does NOT emit the call_graph (that is the L2 child), nor any L3/L4 body statements
or edges. body{} at L1 holds only call nodes.

Additional context

• Emitter approach: walk the existing in-memory model, add a v2 emitter behind a flag; keep v1 emitter as the compat shim during transition.
• One genuinely new datum: thread parser byte offsets into span.bytes.
• Structural interface satisfaction needs method-set matching — cost lives here, not in the resolver.
• Validate each node against the SDK v2 Go models as they land; superset check vs v1 output.
• Schema decisions recorded in repo CLAUDE.md; full transcript in the spec.