fix(core): encode postgres usernames in connection urls

[fcoury]

Fixes #33.
Supersedes #34.

Summary

• encode saved Postgres usernames when building connection URLs
• decode percent-encoded usernames when importing/pasting Postgres URLs
• preserve literal percent sequences such as user%40team

Verification

• cargo test -p tsql --lib connection_to_url
• cargo test -p tsql --lib connection_from_url
• cargo test -p tsql --lib url_paste
• cargo fmt --all
• cargo clippy --all --all-targets -- -D warnings
• cargo test --lib --bins

[Copilot]

Pull request overview

This PR fixes Postgres connection URL handling by percent-encoding usernames when generating URLs and decoding percent-encoded usernames when parsing/pasting URLs, including correct handling of literal percent sequences (e.g., user%40team).

Changes:

• Percent-encode Postgres usernames in ConnectionEntry::to_url().
• Percent-decode usernames in ConnectionEntry::from_url() (used by URL paste/import flows).
• Add regression tests for @ in usernames and literal percent round-tripping, plus a UI URL-paste test.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
crates/tsql/src/config/connections.rs	Encode usernames in generated Postgres URLs; decode usernames when parsing URLs; add targeted tests for encoding/decoding and literal % preservation.
crates/tsql/src/ui/connection_form.rs	Add test ensuring URL paste correctly decodes a percent-encoded Postgres username.

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[Copilot]

to_url() now uses the local urlencoding helper for usernames as well as passwords, but the helper is scoped/named/documented as password-specific (see mod urlencoding comment later in this file). Consider renaming/updating the helper (or its doc comment) to reflect that it encodes general userinfo components, to avoid future confusion/misuse.