feat(portal,server): custom blocks authoring, canvas integration and queued execution

[07prajwal2000]

Closes #258.

Why

Custom blocks worked end to end on the server, but the portal exposed a thin slice: a card grid, a three-field create modal, and an "Open canvas" link. The panel that renders a placed block's settings already read inputParams — nothing could write it, so every custom block on a route was unconfigurable. Authoring a block also gave no way to reach it: it never appeared in the block picker.

What

Authoring

• Input params editor and icon picker, wired into a four-step create page (mirroring the route create flow) and a settings modal, so a block can declare its input contract and be edited after creation. name stays immutable and the UI says why.
• List page reworked: a grid of the real canvas node, search, an empty state, and a click straight into the block's canvas.

Canvas

• Custom blocks load from the DB into the block picker under their own category. Plugin-sourced blocks land in "Built-in", so the shipped set has somewhere to go; empty categories are hidden.
• A placed block renders its own label, description and icon on the node and in the settings panel — the panel titles with the label and shows the identifier underneath, since that is what flows reference.
• On a custom block's own canvas, its integration_selector params are injected into the integration picker. Picking one writes param:<name>; the concrete integration is chosen by the caller, so no test/open action is offered for it. Route canvases are untouched — the behaviour is gated on the custom-block route's blockId.

Engine

• params is bound alongside input in a custom block's JS. Configuration is params.<name> at any depth; input is always the previous block's output. Previously the first block saw config as input.foo and the caller's value at input.input, and the meaning changed further down the graph.

• Nine db/log emitters take their connection through node.value, so a param: integration resolves at call time rather than being baked in.

• New queued invoke mode: durable background execution. async is a floating promise on the request worker — it dies with the worker, competes with traffic, and cannot retry. queued publishes to a JetStream work queue and another worker picks it up.

  One stream for all background work (fluxify.jobs.<projectId>.<kind>), kind-routed through a handler registry, so crons, workflows and scheduled jobs reuse the same stream, consumer and worker rather than each adding a mostly-idle stream. Transport (acks, redelivery, concurrency) lives where NATS is; handlers live where user code is, connected over the existing supervisor↔execution IPC. Tunable via JOBS_CONCURRENCY, JOBS_ACK_WAIT_MS, JOBS_MAX_DELIVER, JOBS_RETRY_DELAY_MS.

Fixes

• The compiler never registered custom blocks into its own library, so any route calling one failed with No codegen for block type. It now registers its own output and resolves dependencies before compiling, and unregisters on rename or delete — a rename previously left the old name resolving to a stale body forever.
• Recursion is refused. A block cannot call itself, directly or through a chain of other custom blocks: checked on every canvas save against the project's call graph (the error names the chain), and reflected in the picker, which offers the block disabled with the reason.
• Handle shape rules no longer depend on stylesheet order — rendering a block preview outside the canvas used to flip the cascade and turn inbound handles into ovals.

Notes

• apps/portal only; no hardcoded colors (semantic tokens throughout); shared components reused.
• Migration: custom blocks whose JS reads a config param as input.foo need params.foo. Nothing warns — the value silently becomes undefined. Cheaper to land now than after people build on it.
• Queued mode needs the compiled worker; the legacy interpreted path never honoured invoke at all.

Testing

turbo run lint clean across all 10 packages. packages/blocks 145 pass, apps/server 355 pass, apps/portal 82 pass.

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