feat: go-to-definition for dependencies in abstract graph classes

[guyca]

vscode-language-server-obsidian: fix cmd-click navigation when the enclosing graph class is abstract (no @graph decorator) and the dependency is declared as an abstract method in a parent abstract class.

Root causes fixed:

• getParentGraphRecursive only recognised classes decorated with @graph. Abstract graph classes without the decorator were invisible to the language server, causing navigation to silently return undefined.
• resolveProvider only searched a graph's own @provides() methods and subgraphs. It never walked the base class chain, so a dependency declared as an abstract method in a parent class could never be resolved.

Changes:

• graphs.ts — getParentGraphRecursive now accepts any enclosing ClassDeclaration as a graph (the isProviderDependency() gate already guarantees we are inside a @provides() method)
• graph.ts — resolveProvider now delegates to the base class via a new resolveProviderOrAbstract path that checks both @provides() methods and abstract method declarations
• New integration test dependencyInAbstractBaseGraph covering the full scenario

react-obsidian: allow @graph decorator on abstract classes

• Added AbstractConstructor type (abstract new (...args: any[]) => any) — a supertype covering both abstract and concrete constructors
• Broadened @graph decorator generic bound from Constructor to AbstractConstructor, making it valid to annotate abstract graph classes (e.g. for ESLint plugin dependency resolution)
• Registration in GraphRegistry is unchanged — harmless on abstract classes since they are never instantiated by the DI runtime
• New acceptance test covering @graph applied directly to an abstract class

eslint-plugin-obsidian: fix false unresolved-provider-dependencies errors on abstract port graphs

• resolveProviders() in graph.ts previously only collected @provides-decorated methods from the base class. Abstract methods without a decorator (the contract pattern used by abstract port graphs) were never added to the provider pool, producing false errors on every provider that consumed them.
• Added resolveBaseGraphProviders() that collects both decorated and abstract methods, recursively walking the full base class chain — mirroring the existing resolveProviderOrAbstract() logic used by the single-name lookup path.
• New valid fixture validGraphWithAbstractBaseProvider.ts covering the pattern.