Emit generic ECMA-335 metadata and IL from symbolic fragments

Parent: #8
Blocked by: #30, #34, #35, and #37

Outcome

Complete the selected symbolic-fragment and fresh-link architecture for generic CLI metadata and executable IL.

Acceptance criteria

• Lowered declarations and methods become immutable symbolic fragments containing stable symbols, labels, locals, exception regions, instructions, and debug contributions.
• Fragments never contain final handles, tokens, heap offsets, method offsets, RVAs, or PE/PDB identities.
• A fresh deterministic public-SRM linker plans rows and layout, resolves references, encodes signatures and bodies, and validates all symbolic operands.
• Assemblies, modules, nested and generic types, fields, methods, properties, events, interfaces, constraints, calls, locals, and exception regions are emitted correctly.
• PEReader, metadata readers, IL verification, runtime consumers, and cross-root deterministic repeats pass.
• Output follows the supplied target references and options rather than the host target framework.
• The selected #7 boundary remains replaceable without leaking encoder state upstream.

Decision inputs

Issue #7; ADRs 0002, 0006, 0009, and 0021.

This issue inherits the corpus-neutral acceptance policy in #8.

Start with parent issue #8, blockers #30, #34, #35, and #37, then review issue #7 and ADRs 0002, 0006, 0009, and 0021. Done means meeting the listed symbolic-fragment and fresh-link acceptance criteria, including deterministic output and passing PEReader, metadata, IL verification, runtime, and cross-root checks.