feat(ontology): add BGBM grinding/metallization modules and promote assembly-process superclass

[JeremyYao1999]

PR: Add BGBM modules + promote assembly-process superclass

Summary

Two additions + one parent-module promotion, all under ontology/ontology/06-osat-packaging-test/00-assembly-processes/:

• Add 03-backside-grinding/ontology.ttl — wafer backside grinding (thinning) semantics
• Add 04-backside-metallization/ontology.ttl — wafer backside metallization (BM) semantics
• Promote 00-assembly-processes/ontology.ttl — replace the placeholder (PlaceholderClass) with a real AssemblyProcess superclass

What's included

Backside grinding (03-backside-grinding)

Class	Description
BacksideGrindingProcess	In-feed wafer backside thinning process
RoughGrindingStep / FineGrindingStep	Coarse vs fine grinding stages
StressReliefStep	Wet-etch / dry-polish / CMP damaged-layer removal
TaikoGrindingProcess	Edge-retained thinning for ultra-thin wafers
BacksideGrindingDefect	Scratch, crack, edge chipping, sub-surface damage, warpage

Properties: hasTargetThickness, hasTotalThicknessVariation (TTV), hasSurfaceRoughness, hasWarpage.

Backside metallization (04-backside-metallization)

Class	Description
BacksideMetallizationProcess	Ohmic backside contact + solderable surface deposition
ElectronBeamEvaporationProcess / SputteringProcess / ElectroplatingProcess	Deposition methods
BacksideMetalStack	Ti / Ni(NiV) / Ag(Au) multi-layer roles
BacksideMetallizationDefect	Peeling/delamination, voids, interdiffusion, oxidation

Properties: hasMetalStack.

Parent module promotion (resolves dangling reference)

00-die-attach and the two new modules all reference assembly_processes:AssemblyProcess, but the parent module was still a placeholder (PlaceholderClass), leaving those references dangling. This PR promotes AssemblyProcess (subclass of semicont-core:ProcessStep) into the parent module, so every assembly sub-process module shares a consistent, resolvable superclass.

Conventions followed

• Turtle (.ttl) under the correct layer/subcategory, per ontology/ontology/README.md.
• owl:versionInfo "0.1.0", prov:wasGeneratedBy curation activity, dc:source / dc:rights, and prov:generatedAtTime provenance on every term.
• Classes subclass assembly_processes:AssemblyProcess (now defined) and reuse semicont-core:Defect / Material / ProcessStep from 00-shared.
• Industry-general knowledge only; no company-specific recipes or vendor differentiation.

Validation

Parsed with rdflib 7.6.0 — no syntax errors, and zero dangling subClassOf references after the parent-module promotion.