docs: polish design documentation and add numerical analysis + workspace pages

[reiase]

Summary

Polishes the Blueprinting design documentation set with two new pages, one IR contract addition, and three small fixes.

New pages (4 files, bilingual)

• docs/design/numerical-analysis.{en,zh}.md — documents the interactive IEEE floating-point format analysis (format layout comparison, bit-level decode, dynamic range, representable values, quantization error, operation range impact) and its place in the analysis architecture as a pure, deterministic presentation analysis view (not a cost provider, not a derived view of canonical IR).
• docs/exploration/workspace.{en,zh}.md — documents the workbench workspace: four modes (point lens / batch lens / evidence lab / numeric lens), shared configuration surface, six testable workspace invariants, and a terminology note clarifying the two distinct meanings of workspace (UI workspace vs WORKSPACE buffer role in PortablePlanIR).

IR contract addition

• docs/design/ir/planning-execution.{en,zh}.md — adds Abstract workspace and conservative bounds subsection under PortablePlanIR: formalizes the three-part obligation (conservative upper bound → target-specific workspace replacement → legality preservation), and notes the current inference slice implementation (workspace-upper-bound / block_working_upper_bound).

Fixes

• providers.md (en/zh): fix broken FrozenDict import path (synthesizer.frozen → schema.frozen)
• modules.md (en/zh): add Not yet callable admonition to ExplorationSession facade example
• numerical-analysis.md: add cross-reference to workload.md for datatype context
• mkdocs.yml: register both new pages in nav (en + zh translations)

Validation

• i18n check: 33 bilingual page pairs validated
• mkdocs build --strict: no warnings