docs(motoko): update guides for new icskills — --default-persistent-actors, inline migration, mops-cli

Background

The icskills submodule is currently pinned at 1d125a9; remote origin/main is at 4713d1e. That commit adds three new skills and substantially rewrites the existing motoko skill:

Skill	Change
motoko	Major overhaul: --default-persistent-actors is now the standard; dot notation (M0236) and implicit comparators (M0237) required; mixins added; moc 1.7.0 pinned
migrating-motoko	New: (with migration = ...) inline syntax for one-shot state migrations
migrating-motoko-enhanced	New: multi-step migration with a migrations/ directory and mops-managed --enhanced-migration flag
mops-cli	New: full toolchain coverage (check, build, test, lint, migrate, toolchain)

Scope

This is a single PR that bumps the submodule from 1d125a9 to 4713d1e and updates the docs to match. The two must ship together: bumping without updating the docs would leave persistent actor in every code example while the pinned skill recommends plain actor {} with --default-persistent-actors.

Required changes

Bump icskills submodule

• Pin .sources/icskills to 4713d1e

Add --default-persistent-actors and drop persistent actor from code examples

With the flag in mops.toml, plain actor { } works and all state is persistent by default. Keeping persistent actor in code examples while recommending the flag is contradictory.

[moc]
args = ["--default-persistent-actors", "-W=M0236,M0237,M0223"]

• Add --default-persistent-actors to the recommended mops.toml setup in guides/backends/data-persistence.mdx, concepts/orthogonal-persistence.md, and guides/canister-management/lifecycle.mdx
• Replace persistent actor with actor in all Motoko code examples (approx. 50 occurrences in 30+ files — grep first to get the full list)
• Keep persistent actor only in explanatory prose where the keyword itself is being discussed

Files known to contain persistent actor in code blocks:

guides/backends/data-persistence.mdx
guides/backends/timers.mdx
guides/backends/certified-variables.md
guides/chain-fusion/bitcoin.mdx
guides/chain-fusion/ethereum.mdx
guides/chain-fusion/solana.mdx
guides/chain-fusion/exchange-rates.mdx
guides/canister-management/lifecycle.mdx
guides/canister-management/cycles-management.mdx
guides/security/canister-upgrades.md
guides/security/access-management.mdx
guides/canister-calls/inter-canister-calls.mdx
guides/canister-calls/parallel-inter-canister-calls.mdx
guides/digital-assets/ledgers.mdx
guides/authentication/internet-identity.mdx
references/application-canisters.md

Document (with migration = ...) inline migration syntax

The canister upgrade guides recommend avoiding preupgrade/postupgrade but say nothing about what to do when a field type changes or a field is renamed. That answer is now the inline migration syntax.

• Add a "Changing persistent state" subsection to guides/canister-management/lifecycle.mdx covering (with migration = ...)
• Update guides/security/canister-upgrades.md to reference the migration syntax for incompatible type changes

Update timer re-registration pattern

guides/backends/timers.mdx uses system func postupgrade to re-register timers. The new skill identifies timer IDs as the canonical transient var use case.

• Update guides/backends/timers.mdx to present transient var as the preferred pattern and move postupgrade to a note for legacy or complex cases

Document mops CLI commands in developer tools

references/developer-tools.md mentions mops but not its primary commands.

• Add coverage of mops check, mops build, mops test, mops lint, and mops migrate to references/developer-tools.md

Out of scope

• postupgrade in certified-variables.md and certification.md: legitimate use for re-establishing certifications after upgrade, not data migration
• docs/languages/motoko/: auto-synced from caffeinelabs/motoko, not manually edited

Prerequisite

Wait for PR #208 to merge before starting. Several affected files are modified by that PR.

Wait for PR #208 to merge, then inspect the .sources/icskills submodule and grep the listed documentation files for persistent actor. Update the recommended Motoko, migration, timer, and mops guidance described in the checklist, and verify the submodule is pinned to 4713d1e with no out-of-scope files changed.